Can people north of 35 degree latitude get enough Vitamin D via the sun in winter?
Check out this answer from Consensus:
People living north of 35 degrees latitude generally cannot obtain sufficient vitamin D from sun exposure during the winter months due to inadequate UVB radiation. To maintain adequate vitamin D levels, individuals in these regions should rely on dietary sources, supplements, and possibly travel to sunnier locations.
Vitamin D is essential for bone health and overall well-being, and it is primarily synthesized in the skin through exposure to ultraviolet B (UVB) radiation from sunlight. However, the ability to produce sufficient vitamin D from sunlight can be influenced by factors such as latitude, season, and time of day. This synthesis aims to determine whether people living north of 35 degrees latitude can obtain adequate vitamin D from sun exposure during the winter months.
Key Insights
- Insufficient UVB Radiation in Winter at High Latitudes:
- Studies indicate that at latitudes above 35 degrees north, there is insufficient UVB radiation during winter months to promote significant cutaneous production of vitamin D3. For example, in Boston (42.2° N) and Edmonton (52° N), no previtamin D3 was produced from November through February and October through March, respectively1 4.
- Populations at high latitudes (e.g., 68° N) experience several winter months with insufficient UV solar radiation to induce significant cutaneous production of vitamin D5.
- Dietary and Supplementary Sources of Vitamin D:
- In regions with limited winter sunlight, dietary intake and supplements become crucial for maintaining adequate vitamin D levels. Studies in Sweden (60° N) and the UK (57° N) show that dietary sources such as fatty fish, fortified dairy products, and vitamin D supplements significantly contribute to serum 25(OH)D concentrations during winter2 6.
- Regular use of vitamin D supplements and travel to sunny locations during winter are important predictors for maintaining adequate vitamin D levels2.
- Impact of Latitude on Vitamin D Synthesis:
- The effectiveness of sunlight in producing vitamin D decreases with increasing latitude. In contrast, regions closer to the equator (e.g., 13.40° N) can produce vitamin D year-round with adequate sun exposure between 11 a.m. and 2 p.m.4.
Can people north of 35deg latitude get enough Vitamin D via the sun in winter?
Reinhold Vieth has answered Extremely Unlikely
An expert from University of Toronto in Nutrition, Vitamins
NO. Human bodies possess a factory that makes vitamin D; it is called the skin. Winter clothing shuts down 95% of that factory (face and hands is only 5% of skin surface). Beyond that, a rule of thumb is that you need the sun to be at least 45 degrees above the horizon (a UV index of at least 3) for it to provide the skin of a white person enough ultraviolet light to make a useful amount of vitamin D.
Bear in mind that skin pigmentation acts like a sunblock, so that a very dark-skin person has the equivalent of SPF 6 sunscreen naturally built into their skin, and needs six times as much ultraviolet light (a combination of sun intensity and/or exposure time) to make the same amount of vitamin D sdas a White person. All populations outside the tropics exhibit declining levels of vitamin D nutrition during winter months. Fortunately, vitamin D disappears slowly out of the body, so our summer gain in vitamin D helps to prevent severe deficiency during winter. The prudent thing is to keep supplementing with vitamin D all year.