If you take daily vitamins, you might be wondering if vitamins raise blood sugar, particularly if you have diabetes. The science is mixed, and more research is needed, but, with some exceptions, several popular vitamins seem to be safe choices if you're watching your blood sugar.
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"Maintaining our blood sugar — or glucose levels — within a healthy range is important, as high levels can cause damage to our kidneys, blood vessels, nerves, eyes and heart," says New York City-based Katrina Hartog, RDN, director of clinical nutrition at Mount Sinai West. And that's even more important for those with diabetes, she says.
"But, there is limited research and inconclusive evidence as to specific vitamin, mineral or herbal supplements that would be the cause of high blood sugars," Hartog says.
If you do have diabetes, it's worth knowing that in a January 2014 position statement on nutrition therapy recommendations published in Diabetes Care, the American Diabetes Association (ADA) discouraged regular vitamin supplementation, as evidence regarding efficacy and long-term safety is lacking.
The ADA also notes that research has been mixed as to whether routine use of such nutrients as vitamin D and magnesium can actually improve blood sugar among people with diabetes. They recommend an overall healthful eating pattern and personalized nutrition therapy.
Still, many people do take vitamins. So here's what research says about the blood sugar effects — or lack thereof — of some popular options.
Read more: The Top Foods High in Vitamins A, B, C, D, E and K
Vitamin B3 (Niacin)
According to the Office of Dietary Supplements (ODS), B3 — aka niacin or nicotinic acid — is essential for healthy metabolism. Nearly all Americans get enough vitamin B3 from their diet, but supplements are available.
Mount Sinai cautions that because niacin supplements may, in fact, increase blood sugar levels, people with diabetes should only take them under the close supervision of their doctor.
The Diabetes Action Research and Education Foundation further warns that in large doses (1,000 milligrams or more per day), niacin can aggravate insulin resistance, drive up blood sugar and ultimately undermine the effectiveness of diabetes control medication. (The daily recommendation is between 14 and 16 milligrams for adults, according to Mount Sinai.)
Known for helping to regulate blood sugar levels, magnesium is critical to the smooth functioning of a wide array of bodily processes, according to the ODS. Dietary sources aren't always sufficient, but most people get enough through food and supplements combined.
The ODS does not specify magnesium as a trigger for high blood sugar, though getting too much magnesium can cause diarrhea, nausea, abdominal cramping and, in extreme cases, even cardiac arrest.
According to the ODS, omega-3 fatty acids are essential to cellular health and an important energy source. There are no daily intake recommendations, and deficiency is very rare. But people with type 2 diabetes considering these supplements should talk to a doctor first, because there's a risk for slight rises in fasting blood sugar, according to Mount Sinai.
That said, it's complicated — because, per the ODS, high-dose omega-3s have sometimes been used to rein in triglycerides. And the National Heart, Lung, and Blood Institute notes that high levels of triglycerides often go hand-in-hand with diabetes. Lowering them could be a win for people with diabetes, though more research is needed.
The ODS generally recommends limiting your intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — two omega-3 fatty acids — to no more than 3 grams per day (including up to 2 grams in supplement form).
As for vitamin C, most people get enough through diet, according to the ODS. Deficiency is rare, though people who smoke or who don't get a lot of variation in their diet may benefit from supplements.
The upper limit is typically considered to be 2,000 milligrams per day for adults, according to the ODS. If you get more C than that, you may face potential side effects like diarrhea, nausea and stomach cramps, but not increased blood sugar.
In fact, a February 2021 meta-analysis in Diabetes Care suggests vitamin C supplementation may even help improve blood sugar control among people with type 2 diabetes, though more research is needed.
- Katrina Hartog, MPH, RD, CDN, director, clinical nutrition, Mount Sinai West, New York, New York
- Office of Dietary Supplements: “Niacin: Fact Sheet for Health Professionals”
- Diabetes Care: “Nutrition Therapy Recommendations for the Management of Adults With Diabetes”
- Diabetes Action Research and Education Foundation: “Vitamin/Mineral Supplementation”
- Office of Dietary Supplements: “Magnesium: Fact Sheet for Consumers”
- Office of Dietary Supplements: “Vitamin C: Fact Sheet for Consumers”
- Office of Dietary Supplements: “Omega-3 Fatty Acids: Fact Sheet for Consumers”
- National Heart, Lung, and Blood Institute: “High Blood Triglycerides”
- Diabetes Care: “Effects of Vitamin C Supplementation on Glycemic Control and Cardiovascular Risk Factors in People With Type 2 Diabetes: A GRADE-Assessed Systematic Review and Meta-Analysis of Randomized Controlled Trials”
- Mount Sinai: “Vitamin B3 (Niacin)”
- Mount Sinai: “Omega-3 Fatty Acids”