Wednesday, August 8, 2012

Too Much Vitamin D?

By now, most people are getting the message loud and clear that--LOW LEVELS OF VITAMIN D ARE NOT HEALTHY. Blood levels need to be maintained above 32 ng/ml and the upper range of "healthy" is often considered to be 80 ng/ml. Low levels not only increase your risk for osteoporosis but also heart disease, cancer, depression, and even death. But how much vitamin D is too much? That is a good question. In my office I like my patient's vitamin D levels to be between 40 and 60 ng/ml, but I know other practitioners differ in their opinions on this subject.

To determine the effects of vitamin D on mortality risk, researchers from the University of Copenhagen studied the vitamin D blood levels of 247,574 subjects. They published their results in a recent paper in the Journal of Clinical Endocrinology and Metabolism (Durup D., et al. 2012). What they found was that both too little and too much vitamin D increase mortality risk. It was determined that blood levels below 10 nmol/liter (that's 4 ng/ml)* raised mortality risk 2.31 times while levels above 140 nmol (56 ng/ml) raised mortality risk 1.42 times. The researchers concluded, "all-cause mortality was observed, indicating not only a lower limit but also an upper limit."

This makes sense, too little of anything, just as too much, is not good. My concern though is with the analysis that levels above 140 nmol (56 raise mortality risk. Please read the response below by Dr. Armin Zitterman. His explanation is helpful and explains why most vitamin D proponents now suggest keeping blood levels between 32 and 80 ng/ml.

*[Note: Conversion for vitamin D: 1.0 nmol/L = 0.4 ng/ml]

Durup D., et al. 2012. A reverse J-shaped association of all-cause mortality with serum 25-hydroxyvitamin D in general practice, the CopD Study. J Clin Endo Metab, doi:10.1210/jc.2012-1176.

In response to the above study, Armin Zitterman from Ruhr University Bochum writes, "Very high 25-hydroxyvitamin D levels may sometimes reflect low availability of the active vitamin D hormone [1,25 dihydroxyvitamin D]. This assumption is in line with experimental data demonstrating that high circulating 25-hydroxyvitamin D levels can be the result of low renal 1 alpha-hydroxylase activity." [1 alpha-hydroxylase is an enzyme produced in the kidney that is often diminished in the elderly due to poor kidney function] Zitterman further explains, "older patients do not only have reduced 1,25 dihydroxyvitamin D levels but also have significantly higher circulating 25-hydroxyvitamin D levels."

Zitterman, A. 2012. Cautious interpretation of the reverse J-shaped association between circulating 25-hydroxyvitamin D and total mortality is necessary. JCEM
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