Diabetes Mellitus

Most people with type 2 diabetes are overweight. Excess abdominal weight does not stop insulin formation,67 but it does make the body less sensitive to insulin. Excess weight can even make healthy people pre-diabetic. Weight loss reverses this problem. In most studies, type 2 diabetes has improved with weight loss.

Increased weight gain in infancy has been associated with a one-and-a half-fold increase in the risk of developing type 1 diabetes in childhood. Being overweight also increases the need for insulin. Therefore, people with type 1 diabetes should achieve and maintain appropriate body weight.

Exercise helps decrease body fat and improve insulin sensitivity. People who exercise are less likely to develop type 2 diabetes than those who do not. People with type 1 diabetes who exercise require less insulin. However, exercise can induce low blood sugar or even occasionally increased blood sugar. Moreover, a preliminary study has shown that long-term physical activity was not associated with control of blood glucose in people with type 1 diabetes. Therefore, people with diabetes should never begin an intensive exercise program without consulting a healthcare professional.

Moderate drinking in healthy people improves glucose tolerance. However, alcohol has been reported to worsen glucose tolerance in the elderly and in people with diabetes in some studies. People with diabetes who drink have also been reported to have a high risk for eye and nerve damage.

Questions remain about where the line should be drawn regarding alcohol intake. For healthy people, light drinking will not increase the risk of diabetes, and may even reduce the risk of developing type 2 diabetes; however, heavy drinking does increase the risk of developing diabetes and should be avoided. People with diabetes should limit alcohol intake to two drinks per day. Total avoidance of alcohol in people with diabetes who are not suffering from alcoholism, liver disease (e.g., cirrhosis), gastritis, ulcers, and other conditions made worse by alcohol might actually be counterproductive. In one report, older people with type 2 diabetes who drank daily, but moderately, had a dramatically lower incidence of deaths from cardiovascular disease compared with nondrinkers. This outcome is not surprising since moderate alcohol intake is associated with protection from cardiovascular disease in most other reports. This finding may be of particular importance because cardiovascular disease is the leading killer of people with diabetes. In another study, nondrinkers had a higher incidence of type 2 diabetes than did moderate drinkers.

People with diabetes who smoke are at higher risk for kidney damage, cardiovascular disease, and other diabetes-linked problems. Smokers are also more likely to develop diabetes; therefore, it is important to quit smoking.

Although most healthcare providers agree on the necessity of self-monitoring of blood glucose (SMBG) by people with type 1 diabetes, disagreement exists within the medical community regarding the efficacy and necessity of SMBG by people with type 2 diabetes. A controlled clinical trial found that home glucose monitoring strips did not affect the management of type 2 diabetes. Moreover, a review of available literature concluded that the efficacy of SMBG in people with type 2 diabetes is questionable and should be tested in a rigorous high-quality trial.

Advocates of SMBG, such as the ADA, have observed that SMBG by people with diabetes has revolutionized management of the disease, enabling them to achieve and maintain specific goals. These observations are well-supported in the medical literature. Detractors point out that indiscriminate use of self-monitoring is of questionable value and adds enormously to healthcare costs. The ADA acknowledges that accuracy of SMBG is instrument- and technique-dependent. Errors in technique and inadequate use of control procedures have been shown to lead to inaccurate test results. Nevertheless, it is likely that self-monitoring of blood glucose, if used properly, can have a positive effect by increasing patient involvement in overall diabetes care. Pharmacists and healthcare practitioners can teach people with diabetes certain skills that will enhance their ability to properly self-manage blood glucose.

The relationship between eating carbohydrates and type 2 diabetes is a complex issue. While eating carbohydrates increases the need for insulin to keep blood sugar normal, diets high in total carbohydrates do not necessarily increase the risk of type 2 diabetes. 2 Researchers have found that diets very high in sugar may worsen glucose tolerance in nondiabetic animals3 and humans. However, the amount of sugar used in these studies in proportion to other foods is much larger than is typically found in human diets.

Years ago, one researcher reported an increase in diabetes among Yemenite Jews who had migrated from a region where no sugar was eaten to one in which they ate a diet including sugar. However, other factors, such as weight gain, may explain the increased risk of diabetes that occurred in this group. Other studies have found no independent relationship between sugar intake and the development of glucose intolerance.

Eating carbohydrate-containing foods, whether high in sugar or high in starch (such as bread, potatoes, processed breakfast cereals, and rice), temporarily raises blood sugar and insulin levels. The blood sugar-raising effect of a food, called its “glycemic index,” depends on how rapidly its carbohydrate is absorbed. Many starchy foods have a glycemic index similar to sucrose (table sugar). People eating large amounts of foods with high glycemic indices (such as those mentioned above), have been reported to be at increased risk of type 2 diabetes. On the other hand, eating a diet high in carbohydrate-rich foods with low glycemic indices is associated with a low risk of type 2 diabetes. Beans, peas, fruit, and oats, have low glycemic indices, despite their high carbohydrate content, due mostly to the health-promoting effects of soluble fiber.

Diabetes disrupts the mechanisms by which the body controls blood sugar. Until recently, health professionals have recommended sugar restriction to people with diabetes, even though short-term high-sugar diets have been shown, in some studies, not to cause blood sugar problems in people with diabetes.15 16 17 Currently, the American Diabetic Association (ADA) guidelines18 do not prohibit the use of moderate amounts of sugar, as long as the goals of normalizing blood levels of glucose, triglycerides, and cholesterol are being achieved.

Most doctors recommend that people with diabetes cut intake of sugar from snacks and processed foods, and replace these foods with high-fiber, whole foods. This tends to lower the glycemic index of the overall diet and has the additional benefit of increasing vitamin, mineral, and fiber intake. Other authorities also recommend lowering the glycemic index of the diet to improve the control of diabetes.

A high-fiber diet has been shown to work better in controlling diabetes than the diet recommended by the ADA, and may control blood sugar levels as well as oral diabetes drugs. In this study, the increase in dietary fiber was accomplished exclusively through the consumption of foods naturally high in fiber - such as leafy green vegetables, granola, and fruit - to a level beyond that recommended by the ADA. No fiber supplements were given. All participants received both the ADA diet (providing 24 grams of fiber per day) and the high-fiber diet (providing 50 grams of fiber per day), for a period of six weeks.

After six weeks of following each diet, tests were performed to determine blood glucose, insulin, cholesterol, triglyceride, and other values. When glucose levels were monitored over a 24-hour period, participants eating the high-fiber diet had an average glucose level that was 10% lower than participants eating the ADA diet. Insulin levels were 12% lower in the group eating the high-fiber diet compared to the group eating the ADA diet, indicating a beneficial increase in the body's insulin sensitivity. Moreover, people eating the high-fiber diet experienced significant reductions in total cholesterol, triglycerides, and LDL cholesterol compared to those eating the ADA diet. They also had slight decreases in glycosylated hemoglobin, a measure of chronically high blood glucose levels.

High-fiber supplements, such as psyllium, guar gum (found in beans), pectin (from fruit), oat bran, and glucomannan have improved glucose tolerance in some studies. Positive results have also been reported with the consumption of 1–3 ounces of powdered fenugreek seeds per day. A review of the research revealed that the extent to which moderate amounts of fiber help people with diabetes in the long term is still unknown, and the lack of many long-term studies has led some researchers to question the importance of fiber in improving diabetes. Nonetheless, most doctors advise people with diabetes to eat a diet high in fiber. Focus should be placed on fruits, vegetables, seeds, oats, and whole-grain products.

Eating fish also may afford some protection from diabetes. Incorporating a fish meal into a weight-loss regimen was more effective than either measure alone at improving glucose and insulin metabolism and high cholesterol.

Vegetarians have been reported to have a low risk of type 2 diabetes. When people with diabetic nerve damage switch to a vegan diet (no meat, dairy, or eggs), improvements have been reported after several days. In one trial, pain completely disappeared in 17 of 21 people. Fats from meat and dairy also contribute to cardiovascular disease, the leading killer of people with diabetes.

Vegetarians also eat less protein than do meat eaters. The reduction of protein intake has lowered kidney damage caused by diabetes and may also improve glucose tolerance. However, in a group of 13 obese males with high blood-insulin levels (as is often seen in diabetes), a high-protein, low-carbohydrate diet resulted in greater weight loss and control of insulin levels, compared with that of a low-carbohydrate diet. Switching to either a high- or low-protein diet should be discussed with a doctor.

Diets high in fat, especially saturated fat, worsen glucose tolerance and increase the risk of type 2 diabetes, an effect that is not simply the result of weight gain caused by eating high-fat foods. Saturated fat is found primarily in meat, dairy fat, and the dark meat and skins of poultry. In contrast, glucose intolerance has been improved by diets high in monounsaturated oils, which may be good for people with diabetes. There is often difficulty in changing the overall percentage of calories from fat and carbohydrates in the diets of people with type 1 diabetes. However, modifying the quality of the dietary fat is achievable. In adolescents with type 1 diabetes, increasing monounsaturated fats relative to other fats in the diet is associated with better control over blood sugar and cholesterol levels. The easiest way to incorporate monounsaturates into the diet is to use oils containing olive oil. However, those who are overweight need to be aware - olive oil is high in calories.

Should children avoid milk to prevent type 1 diabetes? Worldwide, children whose dietary energy comes primarily from dairy (or meat) products have a significantly higher chance of developing type 1 diabetes than do children whose dietary energy comes primarily from vegetable sources. Countries with high milk consumption have a high risk of type 1 (insulin-dependent) diabetes.49 Animal research also indicates that avoiding milk affords protection from type 1 diabetes.

Milk contains a protein related to a protein in the pancreas, the organ where insulin is made. Some researchers believe that children who are allergic to milk may develop antibodies that attack the pancreas, causing type 1 diabetes. Several studies have linked cows' milk consumption to the occurrence of type 1 diabetes in children.

However, other studies have failed to find such a link. One study even reported a protective effect of higher intake of dairy products on diabetes risk in children. One reason for the conflicting results of the research may be that different genetic strains of cows' milk protein (casein) are associated with different levels of risk. Some children who drink cows' milk produce antibodies to the milk, and it has been hypothesized that these antibodies can cross-react with and damage the insulin-producing cells of the pancreas.

Immune problems in people with type 1 diabetes have been tied to other allergies as well, and the importance of focusing only on the avoidance of dairy products remains unclear. Preliminary studies have found that early introduction of cows' milk formula feeding increases the risk of developing type 1 diabetes, although contradictory results have also been published. A study of Finnish children (including full-term children with diabetes) showed that early introduction of cows' milk formula feeding before three months of age (vs. after three months of age) was associated with increased risk of type 1 diabetes. This research supports abstaining from dairy products in infancy and early childhood, particularly for children with a family history of type 1 diabetes. Recent research also suggests a possible link between milk consumption in infancy and an increased risk of type 2 (non-insulin-dependent) diabetes.

Preliminary trials and at least one double-blind trial have shown that large amounts of onion can lower blood sugar levels in people with diabetes.264 265 266 The mechanism of onion's blood sugar-lowering action is not precisely known, though there is evidence that constituents in onions block the breakdown of insulin in the liver. This would lead to higher levels of insulin in the body.267

Medical reports dating back to 1853, as well as modern research, indicate that chromium-rich brewer's yeast (9 grams per day) can be useful in treating diabetes. In recent years, chromium has been shown to improve glucose and related variables in people with glucose intolerance and type 1, type 2, gestational, and steroid-induced diabetes.105 Improved glucose tolerance with lower or similar levels of insulin have been reported in more than ten trials of chromium supplementation in people with varying degrees of glucose intolerance.106 Chromium supplements improve glucose tolerance in people with both type 2107 and type 1 diabetes, apparently by increasing sensitivity to insulin.108 Chromium improves the processing of glucose in people with prediabetic glucose intolerance109 and in women with diabetes associated with pregnancy.110 Chromium even helps healthy people,111 although one such report found chromium useful only when accompanied by 100 mg of niacin.112 Chromium may also lower total cholesterol, LDL cholesterol, and triglycerides (risk factors in cardiovascular disease).113 114

A few trials have reported no beneficial effects from chromium supplementation.115 116 117 All of these trials used 200 mcg or less of supplemental chromium, which is often not adequate for people with diabetes, especially if it is in a form that is poorly absorbed. The typical amount of chromium used in research trials is 200 mcg per day, although as much as 1,000 mcg per day has been used.118 Many doctors recommend up to 1,000 mcg per day for people with diabetes.119

Supplementation with chromium or brewer's yeast could potentially enhance the effects of drugs for diabetes (e.g., insulin or other blood sugar-lowering agents) and possibly lead to hypoglycemia. Therefore, people with diabetes taking these medications should supplement chromium or brewer's yeast only under the supervision of a doctor.

People with diabetes tend to have low magnesium levels.120 Double-blind research indicates that supplementing with magnesium overcomes this problem.121 Magnesium supplementation has improved insulin production in elderly people with type 2 diabetes.122 However, one double-blind trial found no effect from 500 mg magnesium per day in people with type 2 diabetes, although twice that amount led to some improvement.123 Elders without diabetes can also produce more insulin as a result of magnesium supplements, according to some,124 but not all, trials.125 In some trials, insulin requirements are lower in people with type 1 diabetes who supplement with magnesium.126 However, in people with type 2 diabetes who nonetheless require insulin, Dutch researchers have reported no improvement in blood sugar levels.127

Diabetic retinopathy is more likely to occur in magnesium-deficient people with type 1 diabetes.128 In magnesium-deficient pregnant women with type 1 diabetes, the lack of magnesium may even account for the high rate of spontaneous abortion and birth defects associated with type 1 diabetes.129 The American Diabetes Association admits "strong associations...between magnesium deficiency and insulin resistance" but will not say magnesium deficiency is a risk factor.130 Many doctors, however, recommend that people with diabetes and normal kidney function supplement with 200-600 mg of magnesium per day.

Alpha lipoic acid is a powerful natural antioxidant. Preliminary131 132 and double-blind133 134 135 136 137 trials have found that supplementing 600-1,200 mg of lipoic acid per day improves insulin sensitivity and the symptoms of diabetic neuropathy.

Supplementing with 4 grams of evening primrose oil per day for six months has been found in double-blind research to improve nerve function and to relieve pain symptoms of diabetic neuropathy.138

Glucomannan is a water-soluble dietary fiber that is derived from konjac root (Amorphophallus konjac). Glucomannan delays stomach emptying, leading to a more gradual absorption of dietary sugar. This effect can reduce the elevation of blood sugar levels that is typical after a meal.139 After-meal blood sugar levels are lower in people with diabetes given glucomannan in their food,140 and overall diabetic control is improved with glucomannan-enriched diets, according to preliminary141 and controlled142 143 clinical trials. One preliminary report suggested that glucomannan may also be helpful in pregnancy-related diabetes.144 For controlling blood sugar, 500–700 mg of glucomannan per 100 calories in the diet has been used successfully in controlled research.

People with low blood levels of vitamin E are more likely to develop type 1145 and type 2 diabetes.146 Vitamin E supplementation has improved glucose tolerance in people with type 2 diabetes in most,147 148 149 but not all,150 double-blind trials. Vitamin E has also improved glucose tolerance in elderly people without diabetes.151 152 Three months or more of supplementation may be required for benefits to become apparent. The amount used is at least 900 IU of vitamin E per day.

In one of the few trials to find vitamin E supplementation ineffective for glucose intolerance in people with type 2 diabetes, damage to nerves caused by the diabetes was nonetheless partially reversed by supplementing with vitamin E for six months.153 Animal154 and preliminary human155 data indicate that vitamin E supplementation may protect against diabetic retinopathy and nephropathy, serious complications of diabetes involving the eyes and kidneys, respectively, though no long-term trials in humans have confirmed this preliminary evidence.

Glycosylation is an important measurement of diabetes; it refers to how much sugar attaches abnormally to proteins. Vitamin E supplementation reduces this problem in many,156 157 158 159 160 although not all161 162 163 studies.

In one report, vitamin E was found to impair glucose tolerance in obese patients with diabetes.164 The reason for the discrepancy between reports is not known.

Vitamin E appears to lower the risk of cerebral infarction, a type of stroke, in people with diabetes who smoke. A review of a large Finnish study of smokers concluded that smokers with diabetes (or hypertension) represent a subset population that can benefit from small amounts of vitamin E (50 IU per day) without experiencing an increased risk of bleeding.165

People with type 1 diabetes appear to have low vitamin C levels.166 As with vitamin E, vitamin C may reduce glycosylation.167 Vitamin C also lowers sorbitol in people with diabetes.168 Sorbitol is a sugar that can accumulate and damage the eyes, nerves, and kidneys of people with diabetes. Vitamin C may improve glucose tolerance in type 2 diabetes,169 170 although not every study confirms this benefit.171 Vitamin C supplementation (500 mg BID for one year) has significantly reduced urinary protein loss in people with diabetes. Urinary protein loss (also called proteinuria) is associated with poor prognosis in diabetes.172

Many doctors suggest that people with diabetes supplement with 1-3 grams per day of vitamin C. Higher amounts could be problematic, however. In one person, 4.5 grams per day was reported to increase blood sugar levels.173

One study examined antioxidant supplement intake, including both vitamins E and C, and the incidence of diabetic retinopathy (damage to the eyes caused by diabetes).174 Surprisingly, people with extensive retinopathy had a greater likelihood of having taken vitamin C and vitamin E supplements. The outcome of this trial, however, does not fit with most other published data and might simply reflect the fact that sicker people are more likely to take supplements in hopes of getting better. For the present, most doctors remain relatively unconcerned about the unexpected outcome of this isolated report.

Many people with diabetes have low blood levels of vitamin B6.175 176 Levels are even lower in people with diabetes who also have nerve damage (neuropathy).177 Vitamin B6 supplementation has improved glucose tolerance in women with diabetes caused by pregnancy.178 179 Vitamin B6 supplementation is also effective for glucose intolerance induced by birth control pills.180 For other people with diabetes, 1,800 mg per day of a special form of vitamin B6 - pyridoxine alpha-ketoglutarate - has improved glucose tolerance dramatically in some research.181 Standard vitamin B6 has helped in some,182 but not all, trials.183

Biotin is a B vitamin required for glucose metabolism. When people with type 1 diabetes were given 16 mg of biotin per day for one week, their fasting glucose levels dropped by 50%.184 Similar results have been reported using 9 mg per day for two months in people with type 2 diabetes.185 Biotin may also reduce pain from diabetic nerve damage.186 Some doctors try 16 mg of biotin for a few weeks to see if blood sugar levels will fall.

Blood levels of vitamin B1 (thiamine) have been found to be low in people with type 1 diabetes.187 In the 1930s, a trial using 10 mg of vitamin B1 per day for four weeks reported reduced blood sugar levels in six of eleven people with diabetes.188 More recently, administration of both vitamin B1 (25 mg per day) and vitamin B6 (50 mg per day) led to significant improvement of symptoms of diabetic neuropathy after four weeks.189 However, this was a trial conducted among people in a vitamin B1-deficient developing country. Therefore, these improvements might not occur in other people with diabetes. Another trial found that combining vitamin B1 (in a special fat-soluble form) and vitamin B6 plus vitamin B12 in high but variable amounts, led to improvement in some aspects of diabetic neuropathy in 12 weeks.190 As a result, some doctors recommend that people with diabetic neuropathy supplement with vitamin B1, though the optimal level of intake remains unknown.

Coenzyme Q10 is needed for normal blood sugar metabolism. Animals with diabetes have been reported to be CoQ10 deficient. People with type 2 diabetes have been found to have significantly lower blood levels of CoQ10 compared with healthy people.191 In one trial, blood sugar levels fell substantially in 31% of people with diabetes after they supplemented with 120 mg per day of CoQ7, a substance similar to CoQ10.192

In people with type 1 diabetes, however, supplementation with 100 mg of CoQ10 per day for three months neither improved glucose control nor reduced the need for insulin.193 The importance of CoQ10 supplementation for people with diabetes remains an unresolved issue, though some doctors recommend approximately 50 mg per day as a way to protect against possible effects associated with diabetes-induced depletion.

L-carnitine is an amino acid needed to properly utilize fat for energy. When people with diabetes were given L-carnitine (1 mg/kg body weight), high blood levels of fats - both cholesterol and triglycerides - dropped 25–39% in just ten days in one trial.194 In higher amounts (1 gram per day by injection), L-carnitine has been reported to reduce pain from diabetic nerve damage as well.195

People with type 1 diabetes tend to be zinc-deficient,196 which may impair immune function.197 Zinc supplements have lowered blood sugar levels in people with type 1 diabetes,198 though some evidence indicates that zinc supplementation in people with type 2 diabetes does not improve their ability to process sugar.199 Nonetheless, people with type 2 diabetes also have low zinc levels, caused by excess loss of zinc in their urine.200 Many doctors recommend that people with type 2 diabetes supplement with moderate amounts of zinc (15-25 mg per day) as a way to correct for the deficit.

Some doctors are concerned about having people with type 1 diabetes supplement with zinc because of a report that zinc supplementation increased glycosylation,201 generally a sign of deterioration of the condition. This trial is hard to evaluate because zinc supplementation increases the life of blood cells and such an effect artificially increases the lab test results for glycosylation. Until this issue is resolved, those with type 1 diabetes should consult a doctor before considering supplementation with zinc.

Vitamin B12 is needed for normal functioning of nerve cells. Vitamin B12 taken orally, IV, or by injection has reduced nerve damage caused by diabetes in most people studied.202 In a preliminary trial, people with nerve damage due to kidney disease or to diabetes plus kidney disease received IV injections of 500 mcg of methylcobalamin (the main form of vitamin B12 found in the blood) TID for six months in addition to kidney dialysis. Nerve pain was significantly reduced and nerve function significantly improved in those who received the injections.203 Oral vitamin B12 up to 500 mcg TID is recommended by some practitioners.

The intake of large amounts of niacin (a form of vitamin B3), such as 2-3 grams per day, may impair glucose tolerance and should be used by people with diabetes only with medical supervision.204 205 Smaller amounts (500-750 mg per day for one month followed by 250 mg per day) may help some people with type 2 diabetes,206 though this research remains preliminary.

Preliminary trials have shown that niacinamide (another form of vitamin B3) supplementation might be useful in the very early stages of type 1 diabetes,207 though not all trials support this claim.208 209 210 Although an analysis of research shows that niacinamide does help preserve some function of insulin-secreting cells in people recently diagnosed with type 1 diabetes, the amount of insulin required for those given niacinamide has remained essentially as high as for those given placebo.211 A controlled trial found no beneficial effect of niacinamide supplementation (700 mg TID in addition to intensive insulin therapy) on pancreatic function and glucose tolerance in people newly diagnosed with type 1 diabetes.212

Some,213 but not all,214 reports suggest that healthy children at high risk for type 1 diabetes (such as the healthy siblings of children with type 1 diabetes) may be protected from the disease by supplementing with niacinamide. Parents of children with type 1 diabetes should consult their doctor regarding niacinamide supplementation as a way to prevent diabetes in their other children. Although the optimal amount of niacinamide is not known, recent evidence suggests that 25 mg/kg body weight per day may be as effective as higher amounts.215

Vitamin D is needed to maintain adequate blood levels of insulin.216 Vitamin D receptors have been found in the pancreas where insulin is made and preliminary evidence suggests that supplementation can increase insulin levels in some people with type 2 diabetes; prolonged supplementation might also help reduce blood sugar levels.217 Not enough is known about optimal amounts of vitamin D for people with diabetes, and high amounts of vitamin D can be toxic. Therefore, people with diabetes considering vitamin D supplementation should talk with, and have vitamin D status assessed by, a doctor.

Inositol is required for normal neurologic function. Diabetes can cause diabetic neuropathy. This condition has been reported in some, but not all, trials to improve with inositol supplementation (500 mg BID).218

Taurine is an amino acid found in protein-rich food. People with type 1 diabetes have been reported to have low blood taurine levels, a condition that increases the risk of cardiovascular disease by altering blood viscosity. Supplementing with taurine (1.5 grams per day) has restored blood taurine to normal levels and corrected the problem of blood viscosity within three months.219 However, in a double-blind trial, taurine supplementation (2 grams per day for 12 months) failed to improve kidney complications associated with type 2 diabetes.220

Glucose tolerance improves in healthy people taking omega-3 fatty acid supplements.221 Some studies have found that fish oil supplementation improves glucose tolerance,222 high triglycerides,223 and cholesterol levels in people with diabetes.224 However, other studies have found that cholesterol increases225 and diabetes worsens with fish oil supplementation.226 227 228

Until this issue is resolved, people with diabetes should feel free to increase their fish intake, but they should consult a doctor before taking fish oil supplements. Sometimes, such supplementation may be considered. In one trial, people with diabetic neuropathy and diabetic nephropathy experienced significant improvement when given 600 mg TID of purified EPA - one of the two major omega-3 fatty acids found in fish oil supplements - for 48 weeks.229

Doctors have suggested that quercetin might help people with diabetes because of its ability to reduce levels of sorbitol - a sugar that accumulates in nerve cells, kidney cells, and cells within the eyes of people with diabetes - and has been linked to damage to those organs.230 Clinical trials have yet to explore whether quercetin actually protects people with diabetes from neuropathy, nephropathy, or retinopathy.

Vanadyl sulfate, a form of vanadium, may improve glucose control in people with type 2 diabetes,231 232 233 though it may not help people with type 1 diabetes.234 Over a six-week period, a small group of people with type 2 diabetes were given 75-300 mg of vanadyl sulfate per day.235 Only in the groups receiving 150 mg or 300 mg was glucose metabolism improved, fasting blood sugar decreased, and another marker for chronic high blood sugar reduced. At the 300 mg level, total cholesterol decreased, although not without an accompanying reduction in the protective HDL cholesterol. None of the amounts improved insulin sensitivity. Although there was no evidence of toxicity after six weeks of vanadyl sulfate supplementation, gastrointestinal side effects were experienced by some of the participants taking 150 mg per day and by all of the participants taking 300 mg per day. The long-term safety of the large amounts of vanadium needed to help people with type 2 diabetes (typically 100 mg per day) remains unknown. Many doctors expect that amounts this high may prove to be unsafe in the long term.

In a preliminary trial, supplementation with fructo-oligosaccharides (FOS) (8 grams per day for two weeks) significantly lowered fasting blood-sugar levels and serum total-cholesterol levels in people with type 2 diabetes.236 However, in another trial, supplementing with FOS (15 grams per day) for 20 days had no effect on blood-glucose or lipid levels in people with type 2 diabetes.237 In addition, some double-blind trials showed that supplementing with FOS or galacto-oligosaccharides (GOS) for eight weeks had no effect on blood-sugar levels, insulin secretion, or blood lipids in healthy people.238 239 Because of these conflicting results, more research is needed to determine the effect of FOS and insulin on diabetes and lipid levels.

People with diabetes may have low blood levels of manganese.240 Animal research suggests that manganese deficiency can contribute to glucose intolerance and may be reversed by supplementation.241 A young adult with insulin-dependent diabetes who received oral manganese chloride (3-5 mg per day) reportedly experienced a significant fall in blood glucose, sometimes to dangerously low levels. In four other cases, manganese supplementation had no effect on blood glucose levels.242 People with diabetes wishing to supplement with manganese should do so only with a doctor's close supervision.