April 2, 2014
News Review From Harvard Medical School -- 2 Studies: Vitamin D Benefits Still Not Clear
Current evidence still doesn't show any clear benefits from taking vitamin D pills, 2 new reports say. One report looked at hundreds of studies, including those that pulled together results from prior studies. The authors found that vitamin D's effects have been examined closely for only 10 conditions. And there's only enough evidence to say that vitamin D levels could affect 1 of them, the authors said. They found an apparent link between vitamin D levels late in pregnancy and the birth weight of children. The other new study examined previous studies that focused on death rates. Fourteen of the most reliable studies, known as known as randomized controlled trials, found an average 11% lower risk of death among those taking vitamin D3 pills. But death rates were up slightly for people taking vitamin D2. However, these studies were mostly small and included mostly older adults. The journal BMJ published both studies. But an editorial in the same journal said it's not clear whether low vitamin D might cause illness or if the same conditions cause both the illness and the low vitamin levels. Much larger studies are needed, they said. HealthDay News wrote about the reports April 1.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Vitamin D has developed a reputation as a wonder vitamin. But we've seen this sort of enthusiasm before, about vitamin E and other micronutrients. And it appears that once again the accolades probably have been more than this vitamin deserves.
In this week's British Medical Journal, two studies thoroughly evaluated hundreds of "well done" studies on vitamin D. The general conclusion: There's just not enough evidence to say that vitamin D pills prevent heart disease, cancer or many other medical problems. Even as a way to help prevent thin bones (osteopenia and osteoporosis), taking vitamin D alone may not be effective.
It's become a widespread practice for doctors to order vitamin D levels as a routine screening test. The authors of one of the studies question the value of routine testing. They say their findings don't show a major difference in outcomes for young and middle-aged people if they have lower levels of vitamin D. But the authors did find that older people who take vitamin D3 supplements are likely to live longer.
While the evidence doesn't meet the high standard of proof for most health claims, many studies do suggest potential benefits. And low-dose vitamin D supplements are clearly safe.
These studies just add more controversy to the questions experts already debate:
- Who should have a blood test to determine their vitamin D levels?
- Who should take vitamin D supplements?
Expert opinions now vary widely. Here are some common recommendations:
- Test only people who are clearly at high risk of vitamin D deficiency. Examples would include people with thin bones (osteopenia or osteoporosis) and people who never go in the sun and don't eat or drink vitamin D-fortified products.
- Test everyone and advise people based on the result of the blood test.
- Test only those at very high risk of deficiency and have everyone else take a daily vitamin D supplement.
- Use the amount of sunlight exposure and dietary history to determine who should take a supplement.
What Changes Can I Make Now?
For now, I am going to advise my patients based on the recommendation of the Institute of Medicine.
- 600 international units (IU) of vitamin D a day for everyone ages 1 to 70
- 800 IU of vitamin D a day for those 71 and older
Food is the best way to get most vitamins. But not vitamin D. Only a few foods --salmon, tuna, sardines, milk and fortified cereals -- can give you more than 100 IU per serving.
But what about the way humans got vitamin D for millions of years -- from the sun? It's a hot-button issue. Too much exposure to the sun causes skin cancer. That's why so many experts recommend that people take a daily vitamin D supplement.
If you are uncertain that you are getting 600 to 800 IU of vitamin D daily, you could take a supplement. A pill containing 400 to 1,000 IU daily is safe, low-cost insurance. Some studies suggest that vitamin D3 is better than D2.
What Can I Expect Looking to the Future?
Future studies will continue to show varying results on the potential health benefits of vitamin D. But I don't suspect any will show harm from taking low-dose vitamin D pills. Even 2,000 IU daily is well within the safety range.