THE BLOG
01/06/2014 12:47 pm ET Updated Mar 08, 2014

Do You Need to Take Vitamin D?

The New Study: "Vitamin D Status and Ill Health: A Systematic Review."

Half of all American adults take vitamin D supplements. Their goal, of course, is to improve their health. But do those vitamin D pills really help?

In a new study, European researchers performed a systematic review of more than 450 scientific reports focused on the health effects of vitamin D supplements.

Their question: Does taking a vitamin D supplement promote good health and reduce the risk of developing chronic diseases like cancer and heart disease.

Their answer: No.

In otherwise healthy people, taking extra vitamin D provides no health benefits whatsoever.

Contradicts Previous Studies
A large body of scientific evidence links vitamin D deficiency to a whole host of non-skeletal diseases (we'll get to vitamin D and your bones in a moment). When we measure vitamin D levels in sick people, we always find reduced levels. Whether the person has cancer, heart disease, diabetes, dementia, depression, autoimmune disease or virtually any illness, the vitamin D level is low. Hence, the concept that vitamin D deficiency makes people sick. And many doctors take the next step, subscribing to the belief that taking vitamin D will make you well.

Cause and Effect
The authors of the new study conclude that low vitamin D levels are an effect of illness, rather than a cause. The authors arrived at this assertion by examining studies in which people were treated with vitamin D and then examined at intervals to determine whether the vitamin D affected their health status. The results were consistent across virtually all studies. Vitamin D supplements did not reduce the risk of developing health problems.

Why Do Sick People Have Low Vitamin D Levels?
Chronic illnesses cause people to have low vitamin D levels by a variety of mechanisms. Many illnesses are associated with inflammation, and inflammation can lower vitamin D. In addition, sick people often have limited exposure to sunlight (a major source of vitamin D) and low dietary vitamin D intake. Hence, low vitamin D levels are an effect (or consequence) of illness, rather than a cause.

Vitamin D and Bone Health
So far, we have focused on the relationship between vitamin D and overall health. Now let's turn to your bones. There is no question that vitamin D is essential for bone health. Vitamin D helps you absorb calcium, and calcium is critical for bone strength and density. Therefore, adequate intakes of vitamin D and calcium are important. So how do you get enough vitamin D to keep your bones healthy?

Most of our vitamin D comes from sun exposure. Combining ten minutes of sun exposure on your arms and legs two or three times a week with a healthy diet will meet your vitamin D goal. The Institute of Medicine, an expert scientific committee, recommends that most people take in 600 to 800 international units (IU) per day. Because many foods are fortified with vitamin D, this is pretty easy. Few of us require a supplement to achieve this level.

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Can Taking Extra Vitamin D Prevent Osteoporosis?
Many otherwise healthy individuals take vitamin D supplements with the hope of preventing osteoporosis. Don't do it. It doesn't work. Vitamin D supplements do not prevent osteoporosis.

On the other hand, if you already have osteoporosis, you need vitamin D (and calcium supplements), along with special medicines to prevent further bone loss.

Can Too Much Vitamin D Hurt You?
Yes. High dose supplements can increase the risk of kidney stones and, in some people, lead to liver and vascular problems.

The Take-Home Message
Most healthy adults do not need to take vitamin D supplements.

Extra vitamin D does not improve health in those without bone disease.

Get your vitamin D the old fashioned way

  • Sun exposure (in limited quantities)
  • Healthy diet, including foods fortified with vitamin D

Dr. Marc's Medical Minute

Dr. Marc Gillinov is a cardiac surgeon at the Cleveland Clinic and author of Heart 411: The Only Guide to Heart Health You'll Ever Need. He provides expert analysis of the latest medical news and spells out what it means to you.