Could Taking a Supplement Help Lower Blood Sugar?

Research isn’t clear for preventing diabetes

Michael Schroeder,

AARP

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En español

Published August 12, 2023

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A diagnosis of prediabetes — or finding out your blood sugar is elevated — can motivate anyone to consider all their options to prevent full-blown diabetes. For some, that’s meant turning to supplements in hopes of lowering blood glucose. But the evidence for this prevention strategy seems to be somewhat limited — and mixed.

“Certainly, when it comes to vitamins, minerals, supplements and herbs, we have a long history of trying to find something that is going to help. But the sad reality is that the research to date is not as clear-cut,” says Amy Hess-Fischl, registered dietitian and diabetes educator at the University of Chicago Medical Center. “One thing we have to acknowledge about any chronic condition — and certainly diabetes and prediabetes specifically — is that there isn’t really a magic bullet.”

Still, some research has been done to evaluate whether certain supplements could help lower blood sugar in people with prediabetes, whose blood sugar is elevated above a healthy, normal range, putting them at higher risk for diabetes.

If you are thinking of taking a supplement, Hess-Fischl advises talking with your doctor first to make sure that it doesn’t interact with other medications, such as those taken for high blood pressure or cholesterol.

Vitamin D

Perhaps one of the most promising cases being made for taking a supplement to prevent diabetes — for people with prediabetes — involves vitamin D, which doctors frequently recommend to patients to promote healthy bones.

The American Diabetes Association notes that studies have found a link between low vitamin D levels and an increased risk for insulin resistance. Sensitivity to insulin, a hormone secreted by the pancreas, is necessary for cells to absorb — and the body to properly manage — blood sugar and turn it into energy; and insulin resistance is a hallmark of diabetes.

To see if taking a vitamin D supplement would help, researchers analyzed participant data from three different clinical trials and found that adults with prediabetes lowered their risk of developing diabetes by 15 percent when they took a vitamin D supplement. During a three-year follow-up period, 22.7 percent of people with prediabetes who took vitamin D developed diabetes, compared with 25 percent of study participants who were given a placebo.

“The evidence is pretty consistent that vitamin D lowers risk of diabetes in people with prediabetes,” says Anastassios Pittas, M.D., who led the meta-analysis in the Annals of Internal Medicine first published online in February. But the effect, or percentage risk reduction, was lower than the researchers expected based on those previous studies, adds Pittas, chief of endocrinology, diabetes and metabolism at Tufts Medical Center in Boston, who receives funding from the National Institutes of Health to study vitamin D. Another way to put this, according to a summary of the results provided by Pittas and other researchers: “About 30 adults with prediabetes would need to be treated with vitamin D to prevent 1 person from developing diabetes.”

What wasn’t clear from the research is the dose people with prediabetes would need to take to get the optimal effect without taking too much of the supplement.

In the three trials from which Pittas’ team evaluated participant data, those enrolled were given 2,800 to 4,000 international units (or IUs, equivalent to 71 to 100 micrograms) of vitamin D per day. That’s at the upper limit of what’s considered safe, according to the NIH, and well above the average recommended daily amount for adults (which amounts to 600 IUs for people ages 19 to 70 and 800 IUs for adults 71 and older). Too much vitamin D can be harmful and cause issues ranging from nausea and vomiting to dehydration and kidney stones.

More research is needed, including on dosing, as well as to see how individual characteristics such as race and how long a person takes a vitamin D supplement contribute to the outcome, points out Zhenqi Liu, M.D., James M. Moss professor of diabetes at the University of Virginia School of Medicine.

Omega-3

Some research suggests taking an omega-3 supplement could help lower blood sugar, but the data is mixed.

Omega-3 fatty acids are found in salmon and other cold-water fish and are beneficial for brain and heart health. As with vitamin D, which can be derived from the sun’s rays, the optimal way to get omega-3 is from natural sources. But as is also the case with vitamin D, it can sometimes be difficult to get enough omega-3 naturally. Roughly 1 in 13 adults in the United States take a fish oil supplement (or likely did within the last 30 days, based on past survey data), according to the National Center for Complementary and Integrative Health, which is part of the NIH.

One research review published in Critical Reviews in Food Science and Nutrition found that taking an omega-3 supplement helped reduce fasting blood glucose — but not A1C, or glycated hemoglobin, which is a longer-term measure of average blood sugar. The review, which included 30 studies, investigated the effectiveness of taking omega-3 for diabetes treatment and prevention. Another meta-analysis of randomized controlled trials — which are the gold standard in research — found that increasing omega-3 (or omega-6 or total polyunsaturated fatty acids) “has little or no effect” on preventing and treating type 2 diabetes. The review, published in The BMJ, was commissioned by the World Health Organization.

At the same time, a Mediterranean-style diet — which includes seafood high in omega-3 fatty acids — has been shown to help prevent diabetes.

Berberine

One study published in the journal Frontiers found that berberine, a chemical taken from plants such as European barberry and tree turmeric, slowed the progression of prediabetes to diabetes — in rats. Although there has been some human research suggesting it may help with diabetes treatment, researchers say more study is needed.

Side effects can include upset stomach, diarrhea and constipation, and it’s not considered safe for anyone who is pregnant or breastfeeding. Berberine can be transferred across the placenta and in breast milk, and some infants exposed to it developed a type of brain damage called kernicterus.

“There is no clear evidence to support that either omega-3 or berberine supplementation is helpful to prevent diabetes in someone with prediabetes,” Liu contends.

Other supplements

There is a veritable library of supplements — hundreds actually — that some claim will lower blood sugar and help prevent or manage diabetes. But evidence for their effectiveness remains limited. Some of them include:

Cinnamon: One meta-analysis in Complementary Therapies in Medicine found supplementing with cinnamon could help lower fasting blood sugar, but it didn’t affect hemoglobin A1C, a test that measures average blood sugar over two or three months.

Probiotics: These live bacteria and yeasts confer lots of health benefits, from settling the stomach and easing gastrointestinal issues to boosting the immune system. Research shows the “good” bacteria could help the body metabolize glucose and aid in blood sugar control too. A research review in Advances in Nutrition, for example, shows they may help people with type 2 diabetes and prediabetes gain better control of blood sugar. The review included 28 randomized controlled trials in which participants got probiotics from fermented foods such as yogurt and kimchi, so-called functional foods such as honey and bread, and dietary supplements (in capsule or tablet form).

Magnesium: This nutrient helps the body metabolize carbs and manage insulin, and people with diabetes often have a magnesium deficiency. A research review published in the Journal of Human Nutrition and Dietetics suggests taking a magnesium supplement could help lower fasting blood sugar and protect against type 2 diabetes-associated cardiovascular disease.

Check with your doctor — and consider the big picture

Before starting any supplement, you’ll want to discuss with your doctor what you’re considering taking, the dosage and any other medications you’re on. Then regularly check blood sugar to see if it’s actually coming down when you’re taking the supplement.

“Work with your physician and document that this is working,” Pittas says.

A glucose monitor could be used to get lots of objective data on blood sugar levels. Use it for two weeks at a time, then check again in three to six months to see if there’s any change, Pittas says.

Even if a supplement helps lower blood sugar, that doesn’t mean it’s a replacement for a proven diabetes medication.

Diabetes management isn’t simply about blood glucose control. It’s also about reducing a patient’s risk for heart disease and stroke. Supplements, including vitamin D, don’t address that in the way diabetes medications do, Pittas emphasizes.

“At some point, you have to ask yourself, ‘What am I doing?’ ” he says. If regularly taking a supplement such as berberine exposes a person to unknown side effects in the name of diabetes prevention — why not just take metformin, a medication that’s well-studied and has been given to millions of people, Pittas says.

Accordingly, diabetes experts routinely advise a back-to-basics prevention strategy that prioritizes lifestyle changes: 150 minutes per week of exercise, a diet light on processed carbs, shedding pounds if overweight or obese — and taking medication if necessary, rather than relying on supplements.

“We never want to hang our hat on just one thing,” Hess-Fischl says. “That’s why we call it complementary medicine.”

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Michael Schroeder is a freelance health writer and editor who's covered everything from chronic disease and mental health to medication side effects. His stories have been published in a range of print and digital publications, including Time, U.S. News & World Report, The Washington Post, and Psychology Today.