Assessment of the Feasibility of Using Sunlight Exposure to Obtain the Recommended Level of Vitamin D in Canada

Background: Endogenous vitamin D synthesis can be affected by a number of variables, including skin colour, amount of skin exposed and levels of ultraviolet radiation. The objective of this study was to assess the feasibility of using only sunlight exposure in Canada to meet the daily recommended level of vitamin D, given differences in these variables and adherence to guidelines for sun protection.

Methods: Ultraviolet index data for 13 Canadian sites were obtained from Environment Canada. The sun exposure times required to synthesize 1000 IU of vitamin D in fair- and dark-skinned people who exposed either 1/4 or 1/8 of their body surface area to the sun were calculated for each hour of the year. These times were then classified according to whether the ultraviolet index was 3 or more (when sun protection is advised) or less than 3.

Results: During the fall and winter months and in the more northern sites, ultraviolet radiation levels were too low for all skin types to use sun exposure alone to obtain enough vitamin D within one time period. The required exposure time became longer when a smaller surface area was exposed. For people with darker skin, it can be difficult even in the summer to find opportunities outside of when sun protection is advised to use sunlight to obtain the recommended dose of vitamin D.

Interpretation: Although sun exposure is an important source of vitamin D, Canadians should look to other safe sources to meet the body's vitamin D requirements throughout the year.