While a large portion of our nation struggles with vitamin D sufficiency year-round, vitamin D status notoriously dips during the winter, especially for those in higher latitudes.
In the 1980s, professor of medicine, physiology, and biophysics at Boston University medical center Michael Holick, M.D., Ph.D., authored foundational research on vitamin D synthesis2 that has continued to lead the evidence-based conversation on vitamin D throughout seasonal changes.
In this research, Holick discovered the cutaneous vitamin D production (i.e., in the skin) of individuals living in Boston, Massachusetts during winter months was nonexistent. “If you are in Boston in the wintertime and you go outside for 15 minutes, you make zero vitamin D. In fact, you make no vitamin D from about November until the following March,” he previously explained to mindbodygreen.
And while this logic makes sense during the wintertime, sunshine isn’t a sufficient source of vitamin D for most individuals any time of year (even during sunny summer months). Our exposure to sunshine and ability to convert it to vitamin D is impacted by numerous factors—including geographic location, season, climate, UV levels, pollution, clothing, sunscreen, age, and skin tone.
Simply put, we can’t rely on sunlight to achieve and sustain optimal vitamin D levels, especially in the winter. (Hint: This is where vitamin D supplementation comes in.)
