By Matthew Poland and Amy Mullins, MS, RDN
For Floridians, getting enough sunlight during the winter may not be an issue that frequently crosses our sun-kissed minds. However, by spending winter vacation up north or by simply not spending the recommended 10-30 minutes per day outdoors, we could be putting ourselves at risk. In fact, it is estimated that between 20-80% of men and women from the US, Canada and Europe are vitamin D deficient, with rates as high as 45-100% of vitamin D deficiency in some places throughout Asia (1). Even though Florida seems to be as good as it gets for soaking in the sun, a 2005 study of residents of Miami found that between 38-40% were vitamin D deficient (2).
Vitamin D plays a much larger role in our health then we tend to realize. In addition to being a hormone responsible for regulation of bone metabolism, vitamin D has important functions in pregnancy, inflammation, cell growth, neurotransmitter production, immune and neuromuscular function, and glucose metabolism (3). Meanwhile, low vitamin D levels have been associated with increased risk for various diseases including cardiovascular disease, cancer, diabetes, and even an increased risk of mortality (1).
It is well known that sunlight exposure is the major source of vitamin D in our bodies, although some can be absorbed through our diet. However, as we spend less and less time outdoors, our risk of vitamin D deficiency steadily increases. On top of this, there are a variety of factors that can play a role in the ability of an individual to produce vitamin D including skin pigmentation, clothing, sunscreen, and of course where we live. In addition, a likely reason for such a high amount of Miami’s residents being vitamin D deficient is due to the smog levels of larger cities. Air pollution can absorb the UVB rays that our bodies convert into vitamin D, and prevent them from ever reaching us. Plus, in the wintertime, there is less sunlight to be had, which brings into play the next dangerous winter side effect: seasonal affective disorder, appropriately given the acronym, SAD.
While SAD may seem like a northern phenomenon, and it is with up to 9% of Alaska’s residents experiencing SAD compared to Florida’s 1%, it also involves the lack of sunlight during the winter (4). This lack of sunlight interferes with the body’s ability to regulate its circadian rhythm, the 24-hour internal clock that is typically synced with the light-dark cycles of our environment (4). Having shorter days and longer nights in winter is not unique to the north. With some Florida days offering only 10 hours of sunlight and indoor jobs that often consume 8 to 9 hours of our day, there is suddenly limited time to be in the sun (8). Vitamin D has been theorized to play a role in serotonin production, a neurotransmitter responsible for our feelings of well-being and happiness, and the insufficiency or deficiency of vitamin D has also been associated with clinical depressive symptoms (5). In summation, the lack of sunlight during the winter can create depressive symptoms and decreased absorption of vitamin D also leads to further depressive symptoms.
Although this self-perpetuating spiral of doom and gloom may be a bit of a downer, here are a few tips for getting through winter while keeping your vitamin D levels, circadian rhythm, and sanity in check:
- Go outside! Unfortunately, the angle of the sun in the wintertime reduces the availability of ultraviolet sunlight. It is important, however, to spend some time outdoors on sunnier days to allow for vitamin D synthesis, even if it’s not at optimal levels.(6).
- Eat a balanced, healthy diet consisting of a wide variety of foods. Although most foods don’t naturally contain vitamin D, wild-caught salmon and mushrooms being the exceptions, many foods like dairy are fortified with vitamin D (1). However, diet alone has been shown to be insufficient in providing vitamin D to children and adults in the US (7). If through food and sun, your vitamin D levels are not where they need to be, supplementation of around 1000 IUs per day can bring levels back to normal.
- Always talk with your healthcare provider before taking any dietary supplements. Have your vitamin D levels evaluated by your physician. Many people can go throughout life not knowing they are deficient in vitamin D until a broken bone necessitates testing.
So, with winter approaching, keep in mind the importance of being outside and eating well to feel your best as we roll into 2021!
Photo credit: Matthew Poland
Matthew Poland is a Graduate Student in the Department of Food, Nutrition, and Exercise Sciences at Florida State University who is currently working on the Dietetic Internship to become a Registered Dietitian/Nutritionist (RDN).
- Hossein-nezhad, A., & Holick, M. F. (2013). Vitamin D for health: a global perspective. Mayo Clinic proceedings, 88(7), 720–755. https://doi.org/10.1016/j.mayocp.2013.05.011
- Levis S, Gomez A, Jimenez C, et al. Vitamin D deficiency and seasonal variation in an adult South Florida population. J Clin Endocrinol Metab. 2005;90:1557–1562.
- Vitamin D – Fact Sheet for Health Professionals. (2020, September 11). Retrieved September 17, 2020, from https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Melrose S. (2015). Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches. Depression research and treatment, 2015, 178564. https://doi.org/10.1155/2015/178564
- Kerr, D. C., Zava, D. T., Piper, W. T., Saturn, S. R., Frei, B., & Gombart, A. F. (2015). Associations between vitamin D levels and depressive symptoms in healthy young adult women. Psychiatry research, 227(1), 46–51. https://doi.org/10.1016/j.psychres.2015.02.016
- Webb, A. R., Kline, L., & Holick, M. F. (1988). Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. The Journal of clinical endocrinology and metabolism, 67(2), 373–378. https://doi.org/10.1210/jcem-67-2-373
- Moore, C., Murphy, M. M., Keast, D. R., & Holick, M. F. (2004). Vitamin D intake in the United States. Journal of the American Dietetic Association, 104(6), 980–983. https://doi.org/10.1016/j.jada.2004.03.028
- Tallahassee, Florida, USA – Sunrise, Sunset, and Daylength, September 2020. (n.d.). Retrieved September 19, 2020, from https://www.timeanddate.com/sun/usa/tallahassee