Maximizing Winter Health: The Crucial Role of Exercise and Vitamin D

As the days grow shorter and colder, many people in the northern hemisphere experience a seasonal dip in vitamin D levels. This decline happens because our bodies rely on sunlight to convert precursors in the skin into vitamin D, and during fall and winter, sunlight is weaker and less direct. Vitamin D plays a critical role in bone strength, immunity, and overall health—yet deficiencies are common, especially in winter months. In a recent article posted by Peter Attia, MD, researchers did a study on the importance of exercise and Vitamin in the winter months. The study suggests that exercise could help protect against this seasonal decline, giving us one more reason to stay active year-round.

Why Vitamin D Matters

Vitamin D is more than just a “bone vitamin.” Nearly every tissue in the body uses it for essential processes, including immune regulation and cellular function. Sunlight exposure normally provides enough for most people in summer, but colder months mean less skin exposure and fewer opportunities for UV-driven production. People with higher body fat are at even greater risk since vitamin D is stored in fat tissue, reducing its availability in circulation.

The Study: Can Exercise Help?

Researchers in the UK set out to test whether exercise could help offset winter’s typical decline in vitamin D. They recruited 41 sedentary adults with overweight or obesity and divided them into two groups: one group did 10 weeks of supervised cardio training (four sessions per week on treadmills or bikes), while the other group maintained their usual lifestyle. Importantly, participants did not lose weight and were not allowed to take vitamin D supplements—this way, the effect of exercise could be studied in isolation.

At the end of the study, the control group showed the expected seasonal decline in circulating vitamin D levels. In contrast, the exercise group maintained their baseline levels of active vitamin D, despite also experiencing winter’s reduced sunlight. While the effect varied between individuals, the findings suggest that exercise can blunt or even prevent seasonal vitamin D decline.

What This Means for You

Exercise isn’t a replacement for sunlight or supplementation, especially for people at high risk of deficiency (those with obesity, darker skin, or living at high latitudes). But it may serve as a valuable complement to these strategies, helping the body preserve vitamin D while also providing countless other benefits: improved cardiovascular health, better metabolic function, and stronger mental well-being.

The bottom line? As winter approaches, make exercise a non-negotiable. Not only will it keep your heart and mind strong—it may also help keep your vitamin D levels steady through the darker months.