(NaturalNews) Seventy percent of whites and 97 percent of blacks in the United States have insufficient blood levels of vitamin D, according to a study conducted by researchers from Harvard University and the University of Colorado, and published in the journal Archives of Internal Medicine.
Deficiency is defined as any level below 20 nanograms per milliliter, based on guidelines adopted at the 13th Workshop Consensus for Vitamin D Nutritional Guidelines in 2007. Previously, deficiency was defined as less than 11 nanograms per milliliter, but the value was upgraded based on more recent research.
Scientists have known for a long time that insufficient levels of vitamin D can lead to the bone-softening disease rickets in children and can increase the risk of fractures and osteoporosis in adults. More recent research has strongly suggested, however, that even levels that are adequate for bone health may still be too low to protect against heart disease, cancer and autoimmune disorders.
The researchers found that the proportion of people with adequate vitamin D blood levels had dropped 50 percent since the time period between 1988 and 1994. They attributed this effect to people spending more time indoors than ever before, and going out only when protected by high-SPF sunscreen.
Because the body synthesizes vitamin D upon exposure to ultraviolet radiation from sunlight, excessive use of sunscreen can lead to deficiency. Light-skinned people can produce all the vitamin D they need from just 15 minutes of sun on the face and hands per day, while darker skinned people (depending on skin tone) may need up to five times as much sun exposure.