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Vitamin D Needs, Levels Vary Due to Genes and Diet

Madison, Wisconsin - While adequate vitamin D is essential to good health, two new University of Wisconsin School of Medicine and Public Health studies show that individual genetic and environmental differences can influence blood levels of the vitamin.


Vitamin D helps prevent osteoporosis, cancer, diabetes, and heart disease. When the skin is exposed to sunlight, it makes vitamin D, but people who avoid the sun, wear sunscreen or are older can become vitamin D-deficient.


The first study, published recently in the Journal of Nutrition, found that one size doesn’t fit all for vitamin D dosage. It looked at the Institute of Medicine (IOM) recommendation that people age 70 and younger take 600 IU (international units) of vitamin D and people older than 70 take 800 IU a day.


While this recommendation works for most people, it isn’t enough vitamin D for people with several genetic variations. Researchers Dr. Corinne Engelman, assistant professor of population health sciences, and Julie Mares, professor of ophthalmology and visual sciences, looked at people with variations in their genes known to put them at risk for vitamin D deficiency.


Of 288 women aged 70 years or younger who were taking the recommended daily dose, only 66 percent of those with three or four risk genes had the recommended blood concentrations of vitamin D, compared with 91 percent of women with one or none of the risk genes. Of the 102 women over age 70 who took the recommended dose, only half of those with three or four of the risk genes had achieved an adequate vitamin D level, compared with 77 percent of those with none or one of the risk genes.


“If you have none of the risk alleles (genes) the recommended dose is enough, but if we give everyone the same dose, about 40 percent of people with the risk genes won’t be getting an adequate dose of vitamin D,” says Engelman.


“This has important public health ramifications and should lead physicians to tailor their recommendations based on the individual patient. This will be possible in the near future because panels of genes are being developed and used in clinical laboratories and this genetic information will be available to physicians to help them provide better patient care.”


In another study, Engelman and co-author Dr. Javier Nieto, professor and chair of population health sciences, sampled blood from 303 Caucasian volunteers who took part in the Survey of the Health of Wisconsin (SHOW). They wondered whether it made a difference if they tested for regular vitamin Dor a variant known as 3-epi-25(OH)D3, which has recently been detected in blood samples.


They measured vitamin D intake from foods and supplements via a food frequency questionnaire, sun exposure, and waist circumference, and asked questions about diet, exercise and other health habits.


They found that summertime, higher alcohol intake, and higher vitamin D intake from supplements was associated with a higher proportion of 3-epi-25(OH)D3 relative to the total vitamin D. In general, concentrations of the variant tracked with concentrations of overall vitamin D.


“This is basic science, to help answer the question of whether we should be testing for 3-epi-25(OH)D3 and what lifestyle differences are associated with different levels of the variant,” says Engelman, who adds that a second, larger study would be needed to definitely answer that question. That research is being published in the journal Clinical Nutrition.

Date Published: 07/08/2013

News tag(s):  researchpublic health

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Vitamin D Needs, Levels Vary Due to Genes and Diet

Last updated: 07/09/2013
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