Air pollution may increase the risk of vitamin D deficiency

A new study from China suggests that pregnant women living in Beijing are facing a higher risk of vitamin D deficiency as the air has become increasingly polluted in recent years.

The observational study measured blood vitamin D concentrations and surveyed the lifestyle factors of
125 healthy pregnant women (15 to 20 weeks) living in the Chinese capital in winter (1). The study results showed that 97% of participants were vitamin D deficient (less than 50 nmol/L) with 45% being severely deficient (less than 25 nmol/L). Women who reported having longer duration of sun exposure (more than
1.5 hours per day) and who used a multivitamin supplement (vitamin D intakes of 200 to 500 IU per day) had significantly higher but still insufficient vitamin D levels.

The researchers commented that Beijing has experienced serious pollution in recent years. Air pollution inhibits UV-B rays reaching the ground surface, making it more difficult to reach the necessary sun exposure for vitamin D synthesis in skin. In addition, Chinese women avoid direct sun exposure to prevent tanning their skin, as a fair complexion is a cultural preference in China. While the use of pregnancy-specific multi- vitamin supplements can improve the status in women at a low risk of severe vitamin D deficiency, it does not prevent women from vitamin D deficiency during winter. According to the researchers, it seems logical that pregnant women should be routinely supplemented with vitamin D in China. Studies, which systemati- cally reviewed randomized controlled trials and observational studies on maternal vitamin D status in pre- gnancy and the health of the offspring, suggested that an adequate vitamin D supply is likely to have a posi- tive effect on several offspring outcomes such as skeletal health, (race-dependent) risk reduction of low birth weight, type I diabetes and early childhood infections (2, 3).

1. Jun Song S. et al. The High Prevalence of Vitamin D Deficiency and Its Related Maternal Factors in Pregnant Women in Beijing. PLOS One. Published online December 2013.
   
2. Dror D. K. and Allen L. H. Vitamin D inadequacy in pregnancy: biology, outcomes, and interventions. Nutr Rev. 2010; 68:465–477.
   
3. Christesen H. T. et al. The impact of vitamin D in pregnancy on extraskeletal health in children: a systematic review. Acta Obstet Gynecol Scand. 2012; 91:1368–1380.