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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.
|
Vitamin D Source |
Vitamin D Content (IU) |
|
Salmon (wild, 3.5 oz) |
600-1000 |
|
Salmon (farmed, 3.5 oz) |
100-250 |
|
Tuna (canned, 3.6 oz) |
230 |
|
Fortified milk (8 fl oz) |
100 |
|
Fortified orange juice (8 fl oz) |
100 |
|
Fortified yogurt (8 oz) |
100 |
|
Fortified breakfast cereal (1 serving) |
100 |
|
Sunlight: 10 min exposure to arms and legs |
3,000 |
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.
Do Vitamin D Supplements Prevent Other Diseases?
Years ago, doctors found that vitamin D deficiency caused rickets, a bone disease, and that taking vitamin D supplements prevented the problem. This was a nice, tidy package, and many doctors thought that we had the vitamin D equation completely solved. Enamored with this special sunlight-related vitamin, scientists investigated further, finding receptors for it in cells throughout the body, indicating that is purpose might extend beyond bone health. In fact, vitamin D deficiency has been linked to a wide variety of serious illnesses, including various types of cancer, heart disease, diabetes, high blood pressure and autoimmune diseases like multiple sclerosis. These findings raised an important question: could extra vitamin D ward off a whole host of medical problems?
The answer: we don’t know. Thoughtful scientists question whether a single vitamin or chemical could possibly prevent such a wide range of diseases occurring throughout the body. But the absence of scientific evidence has not dampened the public’s love affair with vitamin D. Spurred by media hype and medical hope, Americans spend hundreds of millions of dollars per year on vitamin D supplements.
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Our Conclusions
We don’t have a complete understanding of vitamin D. Based on today’s data, we conclude:
- Most healthy adults do not need vitamin D supplements.
- Ensure adequate vitamin D the old-fashioned way with a diet that includes fortified foods and 10 minutes of sun exposure on your arms and legs (not face) two or three times a week.
- If you can’t get adequate vitamin D from natural sources, ask your doctor about a supplement.
- Avoid mega-doses of vitamin D, as this can cause complications, including kidney stones.
If you have osteoporosis, keep these points in mind:
- The benefits of taking vitamin D supplements (with calcium and other osteoporosis medicines) outweigh the possible risks.
- Remember that smoking, excessive consumption of alcohol, and lack of exercise reduce bone density and make osteoporosis worse.
- Exercise, in particular resistance training, can prevent bone loss and increase bone density.
