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Vitamin D is the “vitamin du jour.” Everybody knows that vitamin D and calcium influence bone health, but in recent years scientists have linked vitamin D to an ever-increasing list of health conditions, ranging from breast cancer to diabetes and heart disease. The more studies and headlines published, the greater the confusion. In 2010, a New York Times story predicted that vitamin D would be the “supplement of the decade.” Was the reporter right? Do you need a daily vitamin D tablet to guarantee your overall health?

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How Much Vitamin D Do You Need?

This seems like a simple question, but scientists and doctors argue forcefully about the answer. Most of our vitamin D comes from sun exposure, but experts agree that some nutritional intake is important. The Institute of Medicine, an expert scientific committee, recommends that most people take in 600 to 800 international units (IU) per day.

Based upon these recommended intakes, the committee concluded that most Americans get enough vitamin D from a standard diet and modest exposure to sunlight.

These conclusions from the Institute of Medicine set off a firestorm of controversy. But the truth is that their recommendations are based upon the scientific evidence that is available. In addition, while doctors often obtain blood tests to measure vitamin D levels, we are not even sure how to define vitamin D deficiency or a normal level.

The bottom line—Until we have more scientific evidence, we can’t recommend wholesale consumption of vitamin D supplements in otherwise healthy people with normal diets and no bone issues. 

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Vitamin D and Bone Health

There is no question that vitamin D is essential for bone health. Vitamin D helps the intestine absorb calcium, and calcium is critical for bone strength and architecture. Osteoporosis is a disorder in which bone density decreases and bone architecture changes, putting the person at risk for fractures, especially of the hip and vertebrae (back). Osteoporosis is distressingly common. If you are currently 50 years old, the chance that you will someday suffer an osteoporosis-related fracture is 50 percent if you are a woman and 13 percent if you are a man. Declining estrogen production after menopause and a lower peak bone mass to start make osteoporosis more prevalent in women.

Can taking extra vitamin D and calcium actually prevent you from developing osteoporosis? Scientific studies addressing this question provide conflicting answers. For now, we can state that adequate dietary intakes of vitamin D and calcium are important for bone health. But we remain unconvinced that vitamin D supplements can 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.