Vitamins for Diabetics: What to Take, What to Test, and What Clashes With Your Meds

Up to 59% of people with diabetes in the US use supplements, by the American Diabetes Association’s estimate. Its 2026 Standards of Care say that without an underlying deficiency, there is no benefit from herbal, vitamin or mineral supplements for people with diabetes. So the useful question about vitamins for diabetics is narrower: which ones your medicines change, and which ones change your medicines.

I built Tavita to check my own long medication list. I’m a kidney patient on dialysis, and I don’t have diabetes. But diabetes is the leading cause of kidney disease, and about 1 in 3 adults with diabetes has kidney disease, according to the NIDDK. So the two lists overlap more than you might think.

This guide is organized by the medicine you take, because the answer to “what should I avoid?” is different on insulin than on metformin alone. Claims link to the drug label, guideline, study or government source they come from. None of it replaces your own care team, so check any change with them first.

What vitamins should diabetics take?

For most people, the guidelines don’t name any. The ADA’s 2026 nutrition chapter says specific supplements are “generally not recommended outside the presence of deficiencies or overt malnutrition.” It makes exceptions for groups who may need a multivitamin:

• Pregnant or breastfeeding people
• Older adults
• Vegetarians and vegans
• People on very-low-calorie or low-carbohydrate diets

What care teams do check is a short list:

• Vitamin B12. Checked if you take metformin.
• Vitamin D. It comes up often, but the ADA says “universal vitamin D supplementation for people with type 1 or type 2 diabetes without deficiency is not recommended.”
• Magnesium. It comes up often too, but the ADA does not recommend magnesium or chromium for blood sugar.

A blood test is how you find out if you’re low.

Vitamins and supplements by diabetes medicine

What the labels and guidelines say, one medicine class at a time. It describes what care teams commonly check, not a plan for you. Timing is in its own table further down.

From the current FDA labels on DailyMed (metformin, glipizide, glimepiride, Lantus, Jardiance, Zestril, Cozaar), the ADA Standards of Care in Diabetes 2026, and the NIH Office of Dietary Supplements fact sheets on chromium and vitamin D. Each row is explained below, with links.

Metformin and vitamin B12

This one has the strongest paper trail: a guideline recommendation, a label warning and a long trial. The metformin label reports that in 29-week trials, about 7% of people with normal B12 dropped to subnormal levels. A possible reason, per the label, is interference with B12 absorption from the B12-intrinsic factor complex in the gut.

How long does it take metformin to lower B12?

It can start within months, and the risk grows with years of use. In the label’s 29-week trials, about 7% of people with normal B12 dropped to low levels; in the longest study, the difference was clear at 5 years. The longest look comes from the Diabetes Prevention Program Outcomes Study. Adults with prediabetes took metformin 850 mg twice a day or a placebo for about 3 years; the metformin group could then keep taking it. B12 was measured at 5 and 13 years. Each year of metformin use was linked to about 13% higher odds of B12 deficiency.

The ADA names who is most at risk:

• People on higher doses (1,500 mg a day or more)
• People on it for 4 to 5 years
• Anyone with anemia, nerve symptoms or chronic kidney disease

The ADA says people who have taken metformin for more than 4 years, or who have other risks such as a vegan diet or past stomach or bowel surgery, should be monitored for B12 deficiency every year. The label’s own interval is every 2 to 3 years. Ask which your doctor follows.

Why it matters: B12 and diabetic neuropathy look alike

Low B12 can cause numbness and tingling in the hands and feet, and the NIH Office of Dietary Supplements notes these symptoms can happen without anemia, so early diagnosis matters to avoid lasting damage. That overlaps with diabetic nerve damage. The ADA says metformin use is linked to worse neuropathy symptoms, which is one reason it suggests testing. The UK drug regulator, the MHRA, lists these among the symptoms:

• Extreme tiredness
• A sore and red tongue
• Pins and needles
• Pale or yellow skin

Should you take B12 with metformin?

The label says the drop “appears to be rapidly reversible” when metformin is stopped or B12 is supplemented. It does not give a dose, and neither does the ADA, which says to “monitor and replete as appropriate.” None of the labels or guidelines we read sets a gap between B12 and metformin either. The label describes a slow effect on absorption, not a clash at the moment you swallow them, and neither the label nor the ADA asks you to space them. Your doctor sets the form and amount if a test comes back low.

Supplements to avoid with diabetes, and why

On insulin or a sulfonylurea: supplements that stack

The glipizide label says low blood sugar is more likely “when more than one glucose-lowering drug is used.” That’s the reason to be careful with anything sold to lower glucose. For chromium, the Office of Dietary Supplements says taking it with insulin “could increase the risk of hypoglycemia,” and that it might add to metformin or other diabetes medicines too.

For herbs, the NCCIH says using cinnamon, St. John’s wort or aloe with diabetes drugs can cause unwanted side effects, and that berberine may interact with some medicines. None of the drug labels we read names berberine or cinnamon specifically. That gap is a reason to ask before starting one. Alcohol belongs here too: the ADA flags delayed lows after drinking, especially on insulin or a sulfonylurea.

What supplements can cause high A1C?

Niacin is the one on the drug labels. The glipizide, glimepiride and Lantus labels all list niacin, or nicotinic acid, among drugs that can raise blood sugar or blunt the medicine. The niacin fact sheet reports that in several trials of high-dose niacin, the kind used for cholesterol at gram-level doses, people taking it had a significantly higher risk of developing diabetes. The labels don’t give a dose at which this starts; see our niacin page for the basics.

On an SGLT2 inhibitor: the risk is the diet

None of the labels or guidelines we read names a vitamin that SGLT2 inhibitors use up. The warning is about eating patterns. The ADA says very-low-carbohydrate plans should be avoided on these drugs because of the risk of ketoacidosis, and that heavy drinking should be avoided and hydration kept up. One practical note from the Jardiance label: these drugs make urine glucose tests read positive, so a urine strip won’t tell you much.

On a GLP-1 medicine

Eating much less changes the math on protein and micronutrients. The ADAasks care teams to monitor people losing weight on purpose for protein and micronutrient shortfalls. We’ve covered this in the GLP-1 nutrition gap and in GLP-1 hair loss.

Supplements the ADA does not recommend

What the ADA says about these supplements:

• Beta-carotene. The ADA counsels against it, because it was linked to higher lung cancer and cardiovascular death risk.
• Vitamin E and C. It says routine supplements are not recommended, given a lack of evidence and long-term safety concerns.
• Fish oil. On fish oil capsules, the same chapter says the evidence does not conclusively support them for preventing or treating heart events in people with diabetes.

What is the best supplement for lowering blood sugar?

None has earned that title. Here is where the usual candidates stand, according to the NCCIH:

• Chromium. Some studies suggest it might help, but they are small and too different from each other to reach clear conclusions.
• Cinnamon. The same mixed evidence. And cassia, the most common cinnamon sold in the US, contains coumarin, which might cause or worsen liver disease.
• Berberine. The same mixed evidence. The berberine studies the NCCIH cites were mostly of Chinese patients, and some were of poor quality.
• Alpha-lipoic acid. It did no better than placebo for blood sugar in a review of 10 studies.

Vitamin D has been tested in a large trial. In D2d, 2,423 adults with prediabetes took 4,000 IU a day or a placebo. After a median 2.5 years, the vitamin D group did not have a significantly lower risk of diabetes. The vitamin D page covers food sources and limits.

Pairs that compete, and one that doesn’t

Each of these is a question for your pharmacist, not a rule to apply yourself.

• Chromium with insulin, metformin or other diabetes medicines, covered above.
• Potassium supplements or potassium salt substitutes with an ACE inhibitor or ARB. The lisinopril label names diabetes as a risk factor for high potassium, and the losartan label advises against using them without consulting a healthcare provider.
• High vitamin D intakes, especially from supplements, might reduce the potency of atorvastatin, lovastatin and simvastatin, according to the ODS vitamin D sheet, because they compete for the same enzyme.
• Glimepiride and colesevelam: the glimepiride label says to take glimepiride at least 4 hours before it.

The pair that doesn’t compete in time is metformin and B12. The label describes a slow effect on absorption, so testing matters more than timing.

Timing: with food or without?

Most diabetes pills have a set relationship to meals. Here is what each label says.

From the metformin, glipizide, glimepiride and Jardiance labels on DailyMed, and ADA Table 9.2. Starting doses on the labels are for prescribers; your dose is the one on your prescription.

Food sources of B12 and magnesium

Magnesium is the clearest case for food over pills. The ODS magnesium sheet explains that high blood sugar raises urine output, so diabetes increases magnesium loss in the urine. People with higher magnesium intakes tend to have a lower risk of type 2 diabetes, but the few small trials of magnesium supplements for type 2 diabetes reported conflicting results. If you do take one, the NCCIH notes the adult upper limit for magnesium from supplements and medicines is 350 mg a day. That limit is for healthy adults; the ODS says the risk of too much magnesium rises when the kidneys don’t work well, so check with your care team first if you have kidney disease. More on our magnesium page.

Vitamin B12 is a different story. Per the ODS, the Daily Value is 2.4 mcg. Here is how some foods compare, with the values from the ODS and USDA data:

• Clams. 3 ounces of cooked clams have about 17 mcg.
• Sockeye salmon. Three ounces have about 3.8 mcg.
• Milk. A cup of 2% milk has about 1.3 mcg.
• Egg. A hard-boiled egg has about 0.6 mcg.

The plant foods in the magnesium chart have no B12 in USDA data. The ADA names a vegan diet as one more reason to test B12 every year on metformin. See the B12 page for more.

Fiber is the other food lever. The ADA asks for at least 14 g of fiber per 1,000 calories from minimally processed carbohydrate foods. Half a cup of boiled lentils has about 7.8 g, and half a cup of black beans about 7.5 g, per FoodData Central. Our fiber page has the rest.

Rich but risky: juice and dried fruit

Whole fruit has a place. The ADA calls whole fruit, fresh, frozen or canned without added sugar, acceptable, and asks people with diabetes to replace sugar-sweetened drinks, including juices, with water or low- or no-calorie drinks. The numbers show why the form matters.

Your kidneys, and other organs to watch

The kidneys come first. The NCCIH notes that kidney disease has been linked to some dietary supplements, which is a particular concern with diabetes, and that anyone with or at risk for kidney disease should have a provider closely monitor their supplements. Metformin is not used when eGFR, the main kidney function number, falls below 30, per the label and the ADA.

Kidney disease also changes the food advice. Look again at the table under the magnesium chart: half a cup of boiled spinach carries about 419 mg of potassium, and an ounce of pumpkin seeds about 330 mg of phosphorus. Juice is similar: a cup of orange juice has about 496 mg of potassium, per USDA data. Once kidney disease is diagnosed, your care team may change how much of these foods makes sense. It even affects testing: the ODS notes that MMA, a sensitive blood marker of B12 status, also rises when the kidneys don’t work well, which can make results harder to read. Our vitamins for kidney disease guide covers that side.

For the liver, two items from above apply: coumarin in cassia cinnamon, and high-dose niacin, where cholesterol guidelines cited by the ODS call for liver enzyme and blood sugar tests before starting. Our vitamins for liver disease guide covers the liver side. For the heart, see the fish oil note above and our vitamins for heart failure guide.

Where Tavita fits

Tavita checks your medicines and supplements against each other. In your profile you can set diabetes to none, prediabetes, type 1 or type 2. With that set, the app:

• cautions when you add chromium, berberine, cinnamon, alpha-lipoic acid, gymnema, bitter melon or fenugreek, with stronger low-sugar wording for type 1 or if insulin or a sulfonylurea is in your list
• cautions on niacin at 500 mg a day or more, because it can raise blood sugar and A1C
• flags chromium with metformin, glipizide, glyburide, glimepiride or insulin
• if you add a B12 supplement alongside metformin, notes that your doctor may want to check your B12 level, and deliberately doesn’t space the two, because timing can’t fix it
• treats a potassium supplement or potassium salt substitute alongside an ACE inhibitor or ARB as a hard stop

The safety check runs the moment you add a supplement, on your phone, free. Prescribed medicines are cautioned, never blocked.

What it isn’t: a glucose tracker or a medical device. It doesn’t log blood sugar or A1C, and it doesn’t set doses. If your care team says something different from the app, follow your care team.

It’s free to start and you don’t need an account. The free plan includes one schedule build a month. Pro rebuilds anytime and costs $12.99 a month or $59.99 a year. Our pill reminder then tells you when each dose is due.

Common questions