Vitamin Supplements: Yes, or No?

A 2023 survey found that 74 percent of U.S. adults take some kind of dietary supplement. Over 90 percent of these users believe such supplements are essential to staying healthy. With a few exceptions, research does not agree.

Vitamins are a very popular form of dietary supplement. In general, we only benefit from vitamin supplements if we have an inadequate intake (usually over a long period of time) or have problems absorbing the nutrient (see Risk for Vitamin Inadequacy box). With the possible exception of vitamin D, inadequate vitamin intake is rare in the United States. Healthy people get all they need from their usual dietary intake.

Let’s take a look at what the latest research says about the risks and potential benefits of vitamin supplements.

Vitamin A.

Diets high in vitamin A and beta-carotene (a pre-form of vitamin A) are associated with lower risk for certain kinds of cancer, but the use of supplements does not appear to help prevent cancer. In fact, taking high doses of betacarotene supplements has been associated with higher risk of lung cancer in smokers, former smokers, and people exposed to asbestos.

High doses of vitamin A from supplements can cause severe headache, blurred vision, nausea, dizziness, muscle aches, bone fracture in older women, problems with coordination, and, in extreme cases, even coma and death. The recommended safe upper limit for vitamin A is 3,000 micrograms (mcg) a day total from foods, beverages, and supplements. (Note that upper limits are well above recommended intake levels. Adverse events may occur if intake is above this limit.)

Vitamin B6 (pyridoxine).

While low blood levels of B6 have been associated higher risk for colorectal cancer, taking supplements has not been shown to prevent cancer or improve outcomes. Taking B6 supplements has not been shown to improve cognitive health. It was once thought that B vitamin supplements could lower risk for heart attack and stroke, but research has shown they do not.

Taking 1,000 milligrams (mg) or more of B6 a day can lead to nerve damage over time. This usually resolves when supplements are stopped. Nausea, heartburn, extreme sensitivity to sunlight, and painful skin patches are also possible. The safe upper limit for vitamin B6 from all foods, beverages, and supplements is 100 mg a day.

Vitamin B12 (cobalamin).

Vitamin B12 supplements are marketed as a way to increase energy and endurance, but this is only true for people who have a B12 deficiency. Research does not support the use of B12 supplements to reduce risk of developing cardiovascular disease or cognitive decline.

Biotin (vitamin B7).

There is little scientific evidence to support marketers claims that biotin supplements can improve the health of hair, skin, and nails. Aside from possibly causing false results on thyroid tests, there are no known harms from biotin supplementation.

Vitamin C.

Contrary to popular belief, research shows that vitamin C supplements do not reduce the risk of getting colds—although routine use might shorten the duration of colds or make symptoms somewhat milder. Dietary patterns high in fruits and vegetables rich in this vitamin are associated with lower risk of lung, breast, and colon cancer. This association may be due to other dietary factors associated with high fruit and vegetable intake, as vitamin C supplements have not been shown to be protective.

Regular use of vitamin C supplements may cause false‐negative results in urine tests used to detect urinary tract infections, and blood or glucose in the urine. The upper limit for intake of vitamin C is 2,000 mg a day. More than this can cause diarrhea, nausea, and stomach cramps.

Vitamin D.

We get vitamin D from sun exposure and some foods, but may not get adequate amounts from dietary intake. Since this vitamin is essential for calcium absorption, low D can impact bone health (although supplementation has not consistently been shown to help with osteoporosis). No benefits of vitamin D supplementation have been identified with regard to cancer, heart disease, depression, and type 2 diabetes prevention. In the body, vitamin D is involved in immune function, but findings on whether supplements help boost immunity have been inconsistent.

Consuming excessive amounts of vitamin D from dietary supplements can cause serious problems, including nausea, muscle weakness, confusion, kidney failure, and irregular heartbeat. The safe upper limit from all foods, beverages, and supplements is 4,000 International Units (IU) a day (100 mcg). It is important not to exceed that level (or get near it unless instructed by a healthcare provider).

Vitamin E.

Deficiency of vitamin E is rare. The best available research finds no benefit from vitamin E supplementation, particularly for preventing coronary heart disease, cancer, or cognitive decline.

High doses of supplements can increase risk of bleeding, hemorrhagic stroke, and prostate cancer. If you consume a supplement, do not take more than 1,000 mg (1,500 IU) a day for natural vitamin E supplements and 1,600 mg (1,100 IU) a day for synthetic vitamin E supplements. A large study found that even 180 mg (400 IU) a day for several years was associated with higher prostate cancer risk.

Folate (vitamin B9).

Low folate status at conception and in the early part of pregnancy can cause neural tube defects like spina bifida in the fetus. Enrichment of wheat flour, cornmeal, and rice in the U.S. with folic acid (a well absorbed synthetic form of folate) has led to a marked decline in cases of this birth defect. No other benefits to folic acid supplementation have been identified.

The recommendation is to limit folic acid/folate from all foods, beverages, and supplements to a maximum of 1,000 mcg (1 gram) a day. Higher doses can mask a vitamin B12 deficiency. High intakes have also been associated with higher risk of colorectal cancer.

Vitamin K.

Eating more vitamin K-rich foods like leafy green vegetables and vegetable oils is associated with strong bones, but studies to date disagree as to whether supplements improve bone strength.

No upper intake limit for vitamin K has been established due to lack of data. People taking warfarin (Coumadin) should follow the advice of their healthcare provider regarding dietary intake of vitamin K-rich foods.

Niacin (vitamin B3).

Very high doses of niacin (in the form of nicotinic acid) lower blood levels of LDL (bad) cholesterol and triglyceride levels and raise levels of HDL (good) cholesterol in people with atherosclerosis—but this has not been consistently found to translate into lower risk for heart attack or stroke. In fact, a new study raises the possibility that excess niacin from supplements may actually increase risk for cardiovascular disease.

High doses can lead to flushing (a temporary reddening of the skin). Thirty milligrams or more of nicotinic acid a day can lead to red, burning, tingling, itchy skin on your face, arms, and chest and cause headaches, rashes, and dizziness.

Pantothenic acid (vitamin B5).

There is little evidence to support the claims made for pantothenic acid supplements. Little is known about the long term effects of high dose pantothenic acid supplementation.

Riboflavin (vitamin B2).

Some healthcare providers recommend riboflavin supplements (at around 400 mg a day) for preventing migraines, although not all studies agree this is helpful. Keep in mind that your body can’t absorb more than about 27 mg of riboflavin at a time, so higher doses of supplements will just be excreted. Adverse effects from riboflavin supplementation are rare.

Thiamin (vitamin B1).

Thiamin supplementation is being studied for Alzheimer’s diseases, heart failure, type 1 and 2 diabetes, and thiamin deficiency in people with alcohol use disorder, but no benefits have been proven. Flushing, hives, itching, weakness, sweating, nausea, and restlessness have been reported with high dose thiamin supplementation.

While most people in the U.S. already get all the vitamins they need from dietary intake, making healthy choices (a variety of plants along with seafood, fat free and low-fat dairy, plant oils, and some eggs, lean meats, and poultry) is the best way to meet all your vitamin needs. It’s practically impossible to get harmful levels of any one nutrient from dietary intake alone!

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