Significance of Sunlight and Vitamin D During the Winter

By: Megan Ng, Graduate Student of Community and Clinical Nutrition at the University of Illinois at Urbana Champaign

Many people know that vitamin D is a nutrient we get through sunlight. However, only taking advantage of the scant days of sunlight within the dark, gray months of winter may not be adequate for your vitamin D needs. This nutrient is even more important given that a large percentage of the population has insufficient or deficient levels (Cantorna, 2020). The risk for deficiency has increased with more people staying indoors, the COVID-19 pandemic, and fears of skin cancer.

Vitamin D plays an essential role in the function and maintenance of our body. It helps our body absorb calcium, which is important for the maintenance of healthy bones (Linus Pauling Institute, n.d.). It also ensures the health of our immune, muscle, and nervous systems (Linus Pauling Institute, n.d.).

Factors that can impact your vitamin D absorption include:

(Webb et al., 2018)

Time of day
Skin color: the darker your skin color the more melanin you have. Melanin is a compound that protects against skin damage and thus synthesizes less vitamin D from the sun
How much skin you expose to sunlight
The further away you live from the equator

Boost With Food

Although the most effective way to maximize vitamin D content and absorption is through sunlight, winter sun rays are a bit different. During the winter months, the ultraviolet (UV) rays tend to be weaker which make it difficult to rely solely on sunshine for vitamin D (Cantorna, 2020). Making sure that you are also including vitamin D in other supplemental forms is key.

In addition to getting some sunlight when you can, some foods supply naturally occurring vitamin D.

These foods include:

(U.S. Department of Health and Human Services, n.d.)

Fatty fish (like salmon, tuna, and sardines)
Cod liver oil
Beef liver
Egg yolks
Some mushrooms that are grown in UV light.

There are also plenty of fortified food sources to choose from:

(U.S. Department of Health and Human Services, n.d.)

Cow’s milk
Soy milk
Some cereals
Orange juice

Using a vitamin D supplement is an option as well, but make sure to check with your health care provider before starting a new supplement. When looking for a supplement, choose vitamin D3 over vitamin D2. Research suggests that vitamin D3 is absorbed more effectively (Balachandar et al., 2021).

Summary

In summary, sunlight is the best way to get vitamin D. This may not be as feasible due to frigid temperatures and environmental conditions. A sizable amount of the population is insufficient or deficient in vitamin D, and wintertime makes it much more difficult to incorporate. Make sure that you are also filling your meals and routines with ways that maximize your ability to get vitamin D.

References

Balachandar, R., Pullakhandam, R., Kulkarni, B., & Sachdev, H. S. (2021). Relative Efficacy of Vitamin D2 and Vitamin D3 in Improving Vitamin D Status: Systematic Review and Meta-Analysis. Nutrients, 13(10), 3328. https://doi.org/10.3390/nu13103328
Cantorna, M. (2020). Why you need more vitamin D in the Winter. The Conversation. Retrieved from https://theconversation.com/why-you-need-more-vitamin-d-in-the-winter-128898
Linus Pauling Institute. (n.d.). Vitamin D. Oregon State University. Retrieved from https://lpi.oregonstate.edu/mic/vitamins/vitamin-D
U.S. Department of Health and Human Services. (n.d.). Vitamin D. NIH Office of Dietary Supplements. Retrieved from https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
Webb, A. R., Kazantzidis, A., Kift, R. C., Farrar, M. D., Wilkinson, J., & Rhodes, L. E. (2018). Colour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes. Nutrients, 10(4), 457. https://doi.org/10.3390/nu10040457