7 Supplements and Vitamins to Avoid if You Are Diabetic

Do you use dietary supplements? Discover the ones you should avoid if you have diabetes.

Merve Ceylan
— Signos
Health Writer & Dietitian
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Reviewed by

Merve Ceylan
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Updated by

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Science-based and reviewed

May 20, 2024
October 2, 2023
— Updated:
October 3, 2023

Table of Contents

Nutrients, including vitamins and minerals, have functions in the physiological process, so their deficiency causes suboptimal health and can be associated with diseases. 

The ADA indicates possible benefits of supplementation for diabetes patients carrying an increased risk of nutrient deficiencies. In this article, you'll find information about dietary supplements that may improve and negatively impact diabetes. 


What Vitamins Should Diabetics Avoid?

Micronutrients (i.e., vitamins and minerals) function as coenzymes and cofactors in metabolic processes, including carbohydrate, protein, and fat metabolism. Therefore, researchers have investigated their effects in preventing and improving diabetes and diabetes complications.

In general, the American Diabetes Association (ADA) does not recommend micronutrient supplementation for people living with diabetes unless deficiency presents. Even if certain dietary supplementation can be recommended, their use is different for diabetes patients than for healthy individuals.¹ 

Diabetes patients are warned about some dietary supplements because their efficiency is not supported by strong evidence or can be harmful. According to the ADA, diabetes patients should consult their doctor before taking chromium, vitamin E, St. John's wort, or niacin supplements.² 

Let's look at a few supplements that diabetes patients should avoid:

  1. Herbal Supplements

The herbal supplement market is vast; unfortunately, their efficiency and risks remain unknown. 

Some herbal supplements diabetes patients should avoid are: ³

  • St. John's wort: This supplement can interact with metformin and anticoagulant (blood-thinning) medications used to treat heart disease. 

St. John's wort supplements can increase the bleeding risk for those using anticoagulant drugs. St. John's wort can also decrease metformin extraction from the kidney (renal clearance). Avoid St. John’s wort if you are taking warfarin, apixaban, dabigatran, heparin, and rivaroxaban.

  • Prickly pear cactus: It's been shown to cause hypoglycemic adverse reactions when used with a diabetes medication. ⁴
  • Ginseng: It can decrease blood clotting. Diabetes patients using blood clotting medications can increase their risk of bleeding. 
  • Cinnamon: Although some studies suggest some benefits, further evidence is needed to prove the supplement's efficiency. 

Cassia cinnamon, the most common cinnamon type sold, contains coumarin, a compound that, if taken in large amounts, can cause issues in people with diabetes and patients with liver disease.⁵

Other herbal supplements that have been researched for their impacts on the diabetic population include bitter melon, some Chinese herbal medicines, fenugreek, ginseng, milk thistle, and sweet potato. However, their safety and efficiency remain inconclusive. 

Diabetes patients should carefully use herbal supplements because they may interact with medications. Any herbal supplement use should be consulted with a healthcare provider.

  1. Vitamin E

Vitamin E is one of the antioxidant vitamins. Antioxidants protect cells by preventing damage caused by harmful substances called free radicals. Diabetes patients may need more antioxidants due to increased free radical production resulting from consistently high blood sugar levels. 

The ADA does not recommend regular vitamin E supplementation for those living with diabetes. However, patients using orlistat may need supplementation because this medication disturbs vitamin E absorption.

Daily supplementation of up to 400 IU is considered to be safe. Vitamin E has anticoagulant properties; a dose of more than >800 IU vitamin E can cause blood clotting, so patients using anticoagulant agents such as warfarin, aspirin, ginkgo biloba, and ginseng can be at increased risk of bleeding.

  1. Chromium

Chromium is a trace element needed for normal glucose metabolism. Although chromium deficiency is rare, it can cause impaired glucose tolerance.  

Chromium affects glucose metabolism through the insulin hormone. It has been shown to increase insulin action by increasing the number of receptors and insulin binding to them. Therefore, insulin can function and lower blood glucose levels.

Research on chromium benefits in people with diabetes shows mixed results; some are promising positive results, and some show it isn't effective. The ADA does not recommend chromium supplementation for diabetes patients. 

Be careful; high doses of chromium can disrupt zinc absorption, iron availability, and cause side effects such as stomach pain, bloating, and skin reactions.

Unfortunately, there is no accurate indicator of chromium deficiency. Your doctor can evaluate the necessity of chromium supplementation based on your body's response to supplementation. Six to twelve weeks of supplementation is suggested to see whether the supplementation benefits an individual.  

  1. Vitamin B3 (Niacin)

Vitamin B3 is found as nicotinic acid and nicotinamide. It has crucial functions in carbohydrate, protein, and fat metabolism. The vitamin treats dyslipidemia, a condition characterized by abnormal blood cholesterol levels.  

The use of niacin is limited in diabetes patients because the vitamin can negatively impact blood glucose levels. 

  1. Omega-3 

The studies that investigated omega-3 fish oil’s effects on diabetes had conflicting results. Some showed fish consumption was associated with lower diabetes incidence, and some indicated the opposite.  

Although no side effects are expected with omega-3 supplementation, diabetes patients using blood-clotting medications should be aware of drug interactions. Omega-3 may interact with blood-clotting medicines. 

  1. Vitamin C

Research mostly shows no benefits of using vitamin C supplementation on the blood glucose levels of diabetes patients. 

  1. Selenium

Selenium is an essential trace element for DNA synthesis and repair, thyroid function, immune support, and antioxidant defense. There is no strong evidence suggesting benefits of selenium supplementation in diabetes patients. Also, long-term intake of high doses of selenium can cause hair and nail loss and problems in the gastrointestinal and nervous systems. 

The use of dietary supplementation should be carefully assessed for diabetes patients. Their medication, complications, diet, and general health status are just a few determinants that influence supplement use, type, dosage, and time. Let's say there are two diabetes patients; one has a higher risk for kidney diseases, and the other has no issues with kidney health. The effective use of supplements would be different.

Kidney disease has been associated with the use of certain dietary supplements. 

Since diabetes is a leading cause of kidney diseases, diabetes patients who have or carry a risk for kidney diseases are advised to consult with their doctor before taking any supplements. ⁶ 

What Vitamins Should Diabetics Take?

Diabetes patients don't need to take dietary supplements if they don't have nutrient deficiencies. However, diabetes patients can carry a risk of nutrient deficiencies due to many factors such as medication use, low-calorie or poor diets, general health status, and lifestyle. 

Let's look at some nutrients that diabetes patients may benefit from:  

Vitamin B6, B9, and B12

Vitamin B6, vitamin B9, and vitamin B12 are involved in homocysteine metabolism. Elevated levels of homocysteine (hyperhomocysteinemia) have been associated with cardiovascular diseases. ²

Some diabetes medications, including biguanide metformin, can decrease the absorption of vitamin B9 and a vitamin B12 deficiency, leading to increased homocysteine levels.

Vitamin B6 deficiency can present because of elderly age, liver disease, dialysis, and some medications such as corticosteroids, isoniazid, and anticonvulsants. 

Diabetes patients using metformin can benefit from periodic control of their blood B6, B9, and B12 levels. If a deficiency is diagnosed, your doctor will prescribe medication or supplement protocol based on your needs.

Vitamin D

Vitamin D is crucial for healthy immune response, skeletal health, and mood regulation. 

Low vitamin D levels have been associated with type 2 diabetes, metabolic syndrome, and insulin resistance. However, vitamin D supplementation didn't improve blood sugar levels for prediabetes patients or decrease the risk of type 2 diabetes, as the results of 35 studies, including a total of 43,407 participants, showed.⁶ 

Although research is inconclusive, the ADA indicates that vitamin D supplementation may be beneficial for diabetes patients who have vitamin D deficiency.²

In diabetes patients, research shows supplementation of some nutrients can be beneficial with relatively small risks of side effects; however, their long-term use is not recommended unless your doctor advises you to take it. 


Magnesium is a cofactor for more than 300 enzymes, including enzymes of energy metabolism. Its deficiency can cause high blood pressure, impaired glucose tolerance, and lipid levels.⁷

Magnesium deficiency is common in diabetic patients. Serum magnesium levels are an indicator of magnesium status. The downside is serum magnesium levels drop when deficiency is severe. 

The ADA advised monitoring the magnesium status of type 1 diabetes and type 2 diabetes patients carrying the risk of deficiency and supplementing it. 

Several forms of magnesium supplementation are available; some research indicates magnesium citrate is more efficient. Although the toxicity of magnesium is rare, doses of up to 350 mg/day can be taken. Higher doses may cause diarrhea and abdominal cramps. 

Alpha-lipoic acid (ALA)

ALA is an omega-3 fatty acid. It has to be taken directly from food sources since the human body can't produce it. 

ALA has been shown to improve diabetic macular edema and diabetic neuropathy, eye conditions that are a complication of diabetes. Diabetes patients with eye problems may benefit from consulting their doctor about ALA supplementation.

Should You Take Supplements for Diabetes?

According to the American Diabetes Association Standards of Medical Care in Diabetes, there is not enough evidence to support the benefits of vitamins, minerals, herbs, and spices supplementation on people with diabetes unless they don't have underlying nutrient deficiencies. ⁸  


Vitamins for Diabetics FAQs

Dietary supplements have a huge market, and both healthy and people with diseases use them to improve health. Since the use of dietary supplements is prevalent, many unanswered questions are in mind. Let's look at some of them:

What are the best supplements for diabetes?

There are no best supplements for all diabetes patients. However, vitamin B6, B9, B12, D, and magnesium deficiency are common in diabetes patients. 

Dietary supplements can help to improve deficiencies. Remember, the best way to utilize dietary supplements is to take them when you need them after getting your doctor's approval.  

Can I take metformin and vitamins at the same time?

Dietary supplements can interact with metformin. Some studies have reported metformin interaction with St. John's wort, prickly pear cactus, and omega-3.  

Remember that many dietary supplements are out there, and the absence of information does not mean that they don't interact with medication. Therefore, always consult with your doctor before taking dietary supplements with metformin at the same time. 

Can people with type 2 diabetes take vitamins?

The ADA does not recommend using dietary supplements unless there is a deficiency to be prevented or cured. A healthy and balanced diet should meet your nutrient needs. 

Can supplements lower blood sugar?  

Some dietary supplements have been shown to improve blood sugar levels. However, there is no strong evidence suggesting the use of dietary supplements to lower blood glucose levels. Diabetes patients should take their medications to control blood glucose levels. 

Can supplements reverse diabetes?

No, dietary supplements can't reverse diabetes. Luckily, healthy living with diabetes is possible with the proper treatment and lifestyle interventions that help you maintain glycemic control.

What precautions should I take when using dietary supplements for diabetes?

First and most important, consult your doctor before taking any supplements. Be informed about potential interactions with your medications.  

Choosing products with third-party testing can be beneficial to be sure the product contains what it claims. 

Lastly, you can monitor your blood sugar levels regularly and report any significant changes to your healthcare provider.

Learn More About How Nutrition Affects Blood Sugar Levels with Signos' Expert Advice 

The Signos CGM system offers continuous blood sugar monitoring so you can know how your body responds to meals in real-time. AI-powered systems provide notifications on glucose spikes and personalized nutrition and exercise plans so you can control blood sugar more efficiently than ever. 

Read Signos' blog to gain insights on diabetes management. You'll find helpful information compiled by experts in the field. 

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Topics discussed in this article:


  1. O’Connell, B. S. (2001). Select vitamins and minerals in the management of diabetes. Diabetes Spectrum, 14(3), 133-148. Doi: https://doi.org/10.2337/diaspect.14.3.133 
  2. Vitamins & Diabetes. American Diabetes Association. Retrieved September  24, 2023 from: https://diabetes.org/healthy-living/recipes-nutrition/vitamins-diabetes
  3. Gupta, R. C., Chang, D., Nammi, S., Bensoussan, A., Bilinski, K., & Roufogalis, B. D. (2017). Interactions between antidiabetic drugs and herbs: an overview of mechanisms of action and clinical implications. Diabetology & metabolic syndrome, 9(1), 1-12. Doi: 10.1186/s13098-017-0254-9 
  4. Sobieraj, D. M., & Freyer, C. W. (2010). Probable hypoglycemic adverse drug reaction associated with prickly pear cactus, glipizide, and metformin in a patient with type 2 diabetes mellitus. Annals of Pharmacotherapy, 44(7-8), 1334-1337. Doi: 10.1345/aph.1P148
  5. Cross, L. V., & Thomas, J. R. (2021). Safety and efficacy of dietary supplements for diabetes. Diabetes Spectrum, 34(1), 67-72. Doi:10.2337/ds19-0068
  6. Diabetes and Dietary Supplements. National Center for Complementary and Integrative Health.  Retrieved September  24, 2023 from: https://www.nccih.nih.gov/health/diabetes-and-dietary-supplements 
  7. Vitamins and Minerals. Diabetes.co.uk. Retrieved September  24, 2023 from: https://www.diabetes.co.uk/vitamins-supplements.html
  8. American Diabetes Association. (2018). 4. Lifestyle management: standards of medical care in diabetes—2018. Diabetes care, 41(Supplement_1), S38-S50. Doi:https://doi.org/10.2337/dc18-S004

About the author

Merve Ceylan is a dietitian and health writer.

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