Wednesday, December 1, 2010

Vitamin D -- Too much or too little?

After writing about health and medicine for more than 20 years, I understand better than most people that scientific research takes time. One study is never the final word on any question.

But even I found myself sputtering while reading today's newspaper about the new study that says we don't need as much vitamin D as we were recently told we did.

In the past year, I began taking vitamin D supplements because of an apparent deficiency that showed up after I had some laboratory blood tests. I've been taking 2,000 international units from supplements. That's in addition to what I get from milk, fortified cereal and other foods, and sunshine.

This latest study says people of my age need no more than 600 units -- so I might have been getting enough already.

Who else is frustrated by this? And tell me what you're doing about it.

I've posted the Associated Press story below in case you hadn't seen it.

Report: A bit more vitamin D is good, not too much

AP Medical Writer

Tuesday, Nov. 30, 2010

WASHINGTON Got milk? You may need a couple cups more than today's food labels say to get enough vitamin D for strong bones. But don't go overboard: Long-awaited new dietary guidelines say there's no proof that megadoses prevent cancer or other ailments - sure to frustrate backers of the so-called sunshine vitamin.

The decision by the prestigious Institute of Medicine, the health arm of the National Academy of Sciences, could put some brakes on the nation's vitamin D craze, warning that super-high levels could be risky.

"More is not necessarily better," cautioned Dr. Joann Manson of Harvard Medical School, who co-authored the Institute of Medicine's report being released Tuesday.

Most people in the U.S. and Canada - from age 1 to age 70 - need to consume no more than 600 international units of vitamin D a day to maintain health, the report found. People in their 70s and older need as much as 800 IUs. The report set those levels as the "recommended dietary allowance" for vitamin D.

That's a bit higher than the target of 400 IUs set by today's government-mandated food labels, and higher than 1997 recommendations by the Institute of Medicine that ranged from 200 to 600 IUs, depending on age.

But it's far below the 2,000 IUs a day that some scientists recommend, pointing to studies that suggest people with low levels of vitamin D are at increased risk of certain cancers or heart disease.

"This is a stunning disappointment," said Dr. Cedric Garland of the University of California, San Diego, who wasn't part of the institute's study and says the risk of colon cancer in particular could be slashed if people consumed enough vitamin D.

"Have they gone far enough? In my opinion probably not, but it's a step in the right direction," added prominent vitamin D researcher Dr. Michael Holick of Boston University Medical Center, who said the new levels draw needed attention to the vitamin D debate and encourage more food fortification.

Vitamin D and calcium go hand in hand, and you need a lifetime of both to build and maintain strong bones. But the two-year study by the Institute of Medicine's panel of experts concluded research into vitamin's D possible roles in other diseases is conflicting. Some studies show no effect, or even signs of harm.

A National Cancer Institute study last summer was the latest to report no cancer protection from vitamin D and the possibility of an increased risk of pancreatic cancer in people with the very highest D levels. Super-high doses - above 10,000 IUs a day - are known to cause kidney damage, and Tuesday's report sets 4,000 IUs as an upper daily limit - but not the amount people should strive for.

And Manson pointed to history's cautionary tales: A list of other supplements - vitamins C and E and beta carotene - plus menopause hormone pills that once were believed to prevent cancer or heart disease didn't pan out, and sometimes caused harm, when put to rigorous testing.

Stay tuned: To help settle the issue, Manson is heading a government-funded study that's recruiting 20,000 healthy older Americans to test whether taking 2,000 IUs of vitamin D really will lower their risk for heart disease, a stroke or certain cancers.

In the meantime, it's hard to consume 600 IUs of vitamin D from food alone. A cup of D-fortified milk or orange juice has about 100 IUs. The best sources may be fatty fish - some servings of salmon can provide about a day's supply. Other good sources are D-fortified cereals.

But here's the report's big surprise: While some people truly are seriously deficient in vitamin D, the average American in fact already has enough circulating in his or her blood - because we also make vitamin D from sun exposure, and because many people already take multivitamins or other D-containing dietary supplements.

Wait a minute: Headlines in recent years have insisted the opposite, that a majority of people don't get enough vitamin D, especially during the winter. What explains the contradiction?

Most testing laboratories are using a too-high cutoff for those blood levels, said report co-author Dr. Clifford Rosen of the Maine Medical Center. The report says at least 20 nanograms is adequate for bone health, while many labs instead list people as low if their blood levels are below 30 ng. Serious vitamin D deficiencies are diagnosed when levels dip well below 20, something that hasn't changed.

Rosen called the state of vitamin D testing "the wild, wild West," and said he hoped that "with this report, we can at least temper people's enthusiasm for just taking tons of supplements."

As for calcium, the report recommended already accepted levels to go along with your daily D - about 1,000 milligrams of calcium a day for most adults, 700 to 1,000 mg for young children, and 1,300 mg for teenagers and menopausal women. Too much can cause kidney stones; the report said that risk increases once people pass 2,000 mg a day.

It's true that most studies link poor health to vitamin D levels that are below 20 ng, said preventive cardiologist Dr. Erin Michos, a Johns Hopkins University School of Medicine professor who wasn't part of the study.

But, "I'm not sure I'm going to dramatically change my practice," said Michos, who pushes her patients to boost their levels until they're between 30 and 50 ng.

EDITOR'S NOTE - Lauran Neergaard covers health and medical issues for The Associated Press in Washington.


Anonymous said...

The assertion that you need more Vit D is based on clinical studies. The assertion that you already get enough is based on a 'report'.

What that means is some doctors did the equivalent of saying "640K is enough RAM for anyone" and published a report.

tarhoosier said...

I do not see where any study mentioned here actually tested the serum level of D, rather than just observing for (apparent) health. In my own case where a 35ยบ latitude residence found serum D3 of 25. After several months of 10,000 i. u./day, with doctor supervision and testing I raised it to 60. 6,000/day now maintains stability. I do not believe any study that does not test the serum levels to determine if sufficiency is attained.

Anonymous said...

There is also no mention of the current thinking linking low vitamin D and MS.

Anonymous said...

I currently take 2,400 of D a day in supplements and my level is right under 40. Before I lower the dosage, I would want to see research that shows the damage of high level of D, as lately it seems most of the research points out positive. I would assume that people process D differently, and some may absorb more than others. I'm keeping my levels for now.

alysse said...

I too was serum tested for D levels and I am always out doors. My was so low they initially prescribed 5k a day. I am now lower, but I found immediate change when taking it, including the fact my allergies and sinuses cleared up because low vitamin d causes inflammation as well. Not one thing will prevent disease including cancer, but all together we are building a healthier immune system. I mean just last week i read the article from the UK where their kids were getting ricketts from lack of D caused by fear of the sun and skin cancer. Too much sunscreen. My doctor told me to get enough vitamin D for me to stay healthy I would need to be outside without sunscreen for 2 hours a day with 70% of my body exposed. Vitamin d levels have been associated with colon cancer. So I will keep taking my D and getting the serum tests to make sure it stays where it needs to be.

Carl K said...

Those recommendations definitely seem to change continuosly.. it can be frustrating..

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