Vitamin D levels in Americans are the highest in August and lowest in February, a new study has found.
Vitamin D or the "sunshine vitamin" primarily keeps bones strong and has been linked to many health benefits. Earlier research has shown that a high intake of vitamin D reduces fracture risk in older adults. Another study had shown that taking Vitamin D and calcium prolongs life and deficiency of the vitamin in diet might lead to depression. The vitamin also keeps mood swings away and prevents weight gain in women who have hit menopause.
The body produces Vitamin D when exposed to ultraviolet B rays of the sun. Certain foods such as egg yolk and fish (mackerel, salmon, sardines and herring) are also a good source of the vitamin. Milk and cereals are generally fortified with vitamin D.
"Even with food fortification, vitamin D levels in the population show a high level of seasonality due to the influence of sunlight," said Amy Kasahara, a UC Irvine graduate student in public health and first author on the paper.
For the study, scientists studied the level of 25-hydroxyvitamin D in 3.4 million blood samples. These samples were collected weekly in the U.S. between July 2006 and December 2011. The study was conducted on a population average basis. The large sample size of the survey provided reliable data on the prevalence of vitamin D in people.
"The exact biochemical pathways from UVB rays to vitamin D were discovered in the 1970s," she added, according to a news release. "In this study, we have shown that vitamin D levels lag the solar cycle, peaking in August and troughing in February."
Researchers add that healthcare providers can measure vitamin D levels of individuals and prescribe vitamin D supplements if necessary.
The study is published in the journal PLOS ONE.