Team McCallum

R&D for Lifetime of Life

Vitamin D v genes?

A study in white males living in the US has concluded that vitamin D levels are 70% determined by genetics in winter but in summer this is replaced by environmental factors, such as sun exposure.

The research, published in the American Journal of Clinical Nutrition, was based on twins from the Vietnam Era Twins (VET) registry, one of the largest in the US, so the men had an average age of 55 when studied.

The men were followed over 12 months to find out the level of vitamin D in their blood in each month, to allow comparison to be drawn between the 6 months aggregated into ‘summer’ and the other 6 called ‘winter’.

Then a standard routine for determining the genetic component was used. Identical twins are assumed to be 100% identical genetically, while for non-identical twins this is 50%. Twins living together are assumed to have a 100% shared common environment, while  those living apart have a unique environment. Blend these into the results, and genetic and environmental components can be teased out.

The researchers from Brazil and the US found that, in general, people with lower blood levels of vitamin D had a larger body mass index, a larger waist-hip ratio (a marker for cardiovascular disease), a higher Framingham risk score (a marker for coronary artery disease) and a higher percentage were diabetic.

And when doing the twins analysis, they found that genetics dominate in winter (70%), but in summer this impact disappeared, and the determinants were environmental, with 53% due to shared environments and 47% due to unique environments.

The team noted other research has found that genetic factors appear to have much less influence in women.

They also raised an interesting point that they did not resolve. Other studies have found that in white people (but not in non-whites), vitamin D levels decrease the further north you live, due to less UVB in sunlight. However, the current team could not find this effect in their subjects, despite the fact that they ranged from 21 degrees N to 49 degrees N.

While the town of Uppsala in Sweden is 60 degrees N. The current study noted previous research in white twins, both male and female,  from Uppsala, which found things worked the opposite way around. That team reported that genetic factors were important in summer, at 48%, but in winter were replaced by a mix of shared and unique environments. Quite why Sweden appears to work in the opposite direction to the US was not explained.

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November 19, 2010 - Posted by | BMI - body mass index, CVD - cardiovascular disease, Diabetes, Genetics, Health, Vitamin D, Waist circumference

1 Comment »

  1. […] Vitamin D v genes? « Team McCallum A study in white males living in the US has concluded that vitamin D levels are 70% determined by genetics in winter but in summer this is replaced by environmental factors, such as sun exposure. Other studies have found that in white people (but not in non-whites), vitamin D levels decrease the further north you live, due to less UVB in sunlight. However, the current team could not find this effect in their subjects, despite the fact that they ranged from 21 degrees . […]

    Pingback by Winter Studies And Summer | November 20, 2010 | Reply


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