Supplement Safety
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The Deal on Supplement Safety

Ever wonder if taking too many supplements can do more harm than good? We’ve rounded up some of the most common supplements to share recommended dosages and precautions.

By Karen Truhe, M.P.H.

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Vitamins and minerals are essential to good health. For most of us, consuming them as part of our daily diet poses no risk. However, before we supplement, it’s important to take several things into consideration.

Luckily, organizations such as the National Institutes of Health Office of Dietary Supplements have made fact sheets available to educate us about vitamins and minerals and to warn us about known health risks with consuming a particular supplement or when using a supplement in combination with certain medications. 

One important distinction is whether a vitamin is fat soluble or water soluble. Fat-soluble vitamins are stored in the liver and tissues, which can build up and cause harm. On the other hand, water-soluble vitamins are not stored. Whatever your body doesn’t use is excreted in the urine.

Let’s look at a few common vitamins and minerals. 

Vitamin A

Vitamin A has a host of benefits. It supports healthy vision, a strong immune system and ensures proper functioning of the heart, kidneys and other organs.

The recommended daily allowance (RDA) is 900 micrograms and 700 micrograms per day for men and women, respectively—which can be obtained by eating vitamin-A rich foods such as leafy green vegetables, dairy, fruits and fortified breakfast cereals.

Vitamin A is fat-soluble, so you can take too much of it. Vitamin A is generally considered safe in daily doses up to 3,000 micrograms per day.

If you are eating a balanced diet and taking a good daily multivitamin, you don’t need to take extra vitamin A unless your doctor recommends it. 

Vitamin C

Vitamin C is a powerful antioxidant that protects the body from free radical damage caused by environmental toxins such as pollution. Vitamin C is also known for its wound-healing abilities and role in collagen production. 

The RDA is 90 milligrams and 75 milligrams per day for men and women, respectively—which you can easily get in your diet from consuming citrus fruits, broccoli and strawberries to name a few.

Popular over-the-counter vitamin C supplements are available in megadoses, and there have been some studies that have shown vitamin C to be effective at reducing the duration of a cold and the severity of symptoms. 

This water-soluble vitamin is safe for adults in doses up to 2,000 milligrams per day.

Vitamin D

Vitamin D is needed for a healthy immune system and for bone strength and is found in cells throughout the body.

The recommended amount per day is 600 IUs for adults. It is almost impossible to get enough vitamin D from diet alone, and the risk of skin cancer outweighs the benefits of basking in the sun sans sunscreen to get your daily dose.

The daily upper limit for adults is 4,000 IU per day. Most doctors recommend a 1,000 IU daily dose to their patients on the low end of the normal scale. If your blood work comes back showing a vitamin D deficiency, your doctor may order a prescription strength dose of vitamin D (10,000 IU/week) to be taken for a short time. 


Iron is a mineral that the body uses to make hemoglobin, a protein in red blood cells that carries oxygenated blood from the lungs to other parts of the body. 

The recommended amount of iron is 8 milligrams and 18 milligrams per day for men and women, respectively—which you can get from eating meat, beans, nuts and fortified breakfast cereals. 

Most adults do not need to take an iron supplement. Too much iron can cause an upset stomach and other gastrointestinal symptoms. If your blood work indicates an iron deficiency, your doctor will advise if an iron supplement is right for you.


Calcium is necessary to maintain strong bones and teeth and for proper nerve and muscle functioning.

The daily recommended amount of calcium is 1,000 milligrams for adults, which you can get from dairy products such as milk, cheese and yogurt. If you avoid dairy, other calcium-rich foods include kale, broccoli and some types of fish.

If you opt to take a calcium supplement, your body may absorb it more readily by taking smaller doses throughout the day.

Older adults require a little extra calcium—around 1,200 milligrams per day. Taken together with vitamin D, this can help reduce the risk of osteoporosis and prevent broken bones.

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