Insufficient vitamin D supply in winter

Current intake recommendations for vitamin D need to be increased by five, says a new study.

According to the new U.S. study (1), in order to achieve vitamin D sufficiency, defined as blood vitamin D levels of at least 75 nanomoles per liter, people of European ancestry with a high sun exposure need 1,300 IU per day of the vitamin during the winter. People of African ancestry with low sun exposure would require much higher intakes, from 2,100 to 3,100 IU per day throughout the year.

Therefore, the researchers ask for increasing the intake recommendations up from the current adequate intakes set at 5 micrograms per day (200 International Units).

Some experts define an optimal vitamin D status as at least 100 nanomoles per liter (nmol/L) of 25(OH)D. Vitamin D deficiency is defined by some as 25(OH)D levels below 50 nmol/L. In adults, it is said vitamin D deficiency may precipitate or exacerbate osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.

Concerns are growing over the health implications of living with insufficient and deficient vitamin D levels. A recent study from China reported that 94 percent of people aged between 50 and 70 enrolled in the study were vitamin D deficient or insufficient, which may increase their risk of metabolic syndrome.

While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.

1. Hall L.M. et al. Vitamin D Intake Needed to Maintain Target Serum 25-Hydroxyvitamin D Concentrations in Participants with Low Sun Exposure and Dark Skin Pigmentation Is Substantially Higher Than Current Recommendations. Journal of Nutrition. January 2010.