Twins reduction in vitamin D in the winter or summer - Nov 2010

Heritability and seasonal variability of vitamin D concentrations in male twins.

Am J Clin Nutr. 2010 Oct 13.
Karohl C, Su S, Kumari M, Tangpricha V, Veledar E, Vaccarino V, Raggi P.
Departments of Medicine and the Division of Endocrinology, Metabolism and Lipids, Department of Medicine, Emory University, Atlanta, GA, and the Division of Nephrology, Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.

BACKGROUND: Serum 25-hydroxyvitamin D 25(OH)D concentrations can be affected by several environmental and individual factors. It is not clear to what extent genetic influences play a role in determining vitamin D status. Thus far, studies on the heritability of vitamin D have provided conflicting results.

OBJECTIVE: We estimated the heritability of vitamin D concentrations and the effect of season on heritability estimates.

DESIGN: We measured serum 25(OH)D concentrations in 510 middle-aged, male twins (310 monozygotic and 200 dizygotic twins) selected from the Vietnam Era Twin Registry. Generalized estimating equations were used to test the association between 25(OH)D and other study factors. Structural equation modeling was used to estimate the heritability of 25(OH)D.

RESULTS: The twins' mean (±SD) age was 55 ± 2.8 y. The mean (±SD) 25(OH)D concentration was 38.4 ± 23.3 ng/mL with a substantial seasonal variation (a 6.1-ng/mL lower value during the winter than during the summer, P = 0.003). Approximately 70% of the variation in 25(OH)D concentrations during the winter was explained by genetic factors. However, in the summer, 25(OH)D concentrations were not heritable. During the summer, 53% of the variation in 25(OH)D concentrations was due to shared environmental factors, and 47% of the variation in 25(OH)D concentrations was due to unique environmental factors.

CONCLUSIONS: Serum 25(OH)D concentrations are highly heritable during the winter season only. In the summer, environmental conditions (eg, sun exposure) prevail over genetic backgrounds in determining serum 25(OH)D concentrations. This trial was registered at as NCT00017836. PMID: 20943799

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70% of the change of vitamin D during the winter appears to be due to genetics

For 55 year-old white males who were in Vietnam Era Twin Registry at 39 degrees North

Perhaps the genetic factor would not have been as strong if they had studied twins living near the equator, due to less magnetic variations there.

Study with opposite conclusion Genes account for half of SUMMER variability in vitamin D - Nov 2009 at VitaminDWiki

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Interesting to see the factors associated with lower level of vitamin D in this study

  • Smoking - more, but only somewhat related
  • HDL low (which is needed to make vitamin D)
  • Framingham risk score much higher
  • Hypertension much higher
  • Diabetes much higher


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