Vitamin D: How much is too much?
Published: Saturday, January 8, 2011 at 3:00 a.m.
Last Modified: Tuesday, January 4, 2011 at 3:35 p.m.
Has all the talk about the importance of Vitamin D been hype?
The Institute of Medicine’s Food and Nutrition Board recently published their report on vitamin D — its proven effects on health and the new recommended daily requirements. (The institute is an independent, nonprofit organization established in 1970 as the health arm of the National Academy of Sciences.)
On first read, the report appears that they are saying that D is not beneficial for anything other than bone health, that we don’t need all that much D, and that too much Vitamin D can be dangerous.
Is it true that a higher level of vitamin D is not helpful to the immune system, unnecessary for pregnant women or infants, and not the anti-cancer agent we thought?
It helps to understand that the Institute of Medicine (IOM) is a careful, conservative organization. They are unable to make definitive statements to the American public based on anything less than undeniable proof. While there is plenty of data linking vitamin D to beneficial health effects other than bone health, so far only the bone studies are considered gold-standard. This is because they are randomized, placebo-controlled, double-blinded clinical trials.
Gold-standard research is carefully controlled to avoid any unscientific influences on the data. Scientists randomly select the study participants and secretly give some patients placebos and some the real Vitamin D. By designing the study this way, they are able to say that the results are unaffected by anyone’s opinions or expectations.
Gold-standard studies take years to complete. While further data is being collected, we can wisely look at the preliminary information and know quite a bit about vitamin D.
There is an increasingly large amount of scientific data linking low levels of vitamin D to many aspects of health: immune function, several cancers, diabetes, arthritis, pregnancy complications, and other common disease states. Although we can’t be certain that it is lack of Vitamin D that is causing these health problems to occur, we do see that they are strongly connected.
What about toxicity? Too much vitamin D can cause complications, but it takes extremely high doses. Several exhaustive reviews by experts have clearly shown that most individuals would have to take at least 10,000 to 40,000 IUs (International Units) of cholecalciferol (vitamin D3) every single day for many weeks, or even months, before showing signs of overdose.
Still, it is good to check with a knowledgeable physician before aggressively restoring your levels of vitamin D. There are some specific health conditions that can cause individuals to be hypersensitive to D. In these individuals, too much D produces too much calcium in the blood (hypercalcemia). Simple blood tests can identify hypercalcemia, which is usually reversible when the supplements are discontinued.
We all require lower doses of calcium supplements when taking adequate amounts of vitamin D. The Harvard School of Public Health surprisingly found that low-dose calcium (500mg/day) combined with vitamin D supplements decreased the numbers of fractures in people with osteoporosis. But those taking higher doses (1000 mg or more) did not benefit. Less calcium and more D3 seems to be ideal for bone health.
It is a rare individual who cannot safely take at least 2000 IUs of vitamin D3 daily. Our bodies use up 4000 IUs each day for regular body functions, and taking half of that as a supplement is not going to harm most individuals. Many may need to take significantly more to replenish chronic low levels of D3. It is especially important for pregnant women and children to have adequate levels of vitamin D, because it can affect their health now and for years to come.
The best course is to get your 25-OH blood levels checked at a lab. This is a simple blood test that measures the nanograms of active vitamin D per milliliter of blood. If your level is less than 50ng/ml, consider supplementing with D3. The current data is compelling, and your body will benefit in ways still being proven. While further research is ongoing, there is much to gain by making sure you have enough D3 for good health.
Read what the Harvard School of Public Health has to say about vitamin D:
http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/vitamin-d/index.html
Dr. Stacey Kerr, a longtime Sonoma County family physician, graduated from UC Davis Medical School and has been certified in her specialty by the American Board of Family Medicine. Her columns are not intended as a substitute for hands-on medical advice or treatment. Consult your health care provider before adhering to any recommendations in this column. Email comments to drkerr@the-doctors-inn.com.
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