Vitamin D and its Role in Winter Months

As fall and winter arrive, we are exposed to less sunlight, which often leads to lower vitamin D levels. Vitamin D is important because it helps keep our bones strong and our immune system working well. Many people already have low vitamin D and this tends to get worse in the winter. A research team wanted to see if regular cardio exercise (like walking on a treadmill or riding a bike) could help stop vitamin D levels from dropping during the winter.

Normally, our bodies make vitamin D when sunlight hits our skin. In the summer, just a few minutes of sun on part of the body can be enough especially for people with lighter skin. But in winter, the sun is weaker, days are shorter, and we wear more clothes, so we don’t make as much vitamin D. The problem can be worse for people with more body fat, because vitamin D gets stored in fat tissue and is less available in the blood. People with obesity have a much higher risk of vitamin D deficiency.

In a recent study published in Advanced Science, adults with overweight or obesity were split into two groups for 10 winter weeks: an exercise group and a control group. The exercise group did four cardio workouts per week at an indoor gym, while the control group kept their usual lifestyle. No one was allowed to take vitamin D supplements or change their diet or weight much, so the scientists could focus on the effect of exercise alone. By the end of the study, the control group’s levels of active vitamin D had dropped by about 15%, but the exercise group kept their levels about the same.

The results suggest that exercise can help slow or prevent the usual winter drop in vitamin D, especially for the active form that the body uses most. However, exercise did not completely stop all vitamin D from decreasing, and the exact reasons why it helps are still not fully understood. The main takeaway is that exercise should not replace vitamin D supplements or good food sources, especially for people at high risk of deficiency, but it can be a helpful extra tool. Overall, this is one more reason to stay active during the winter—not just for your heart, mood, and metabolism, but also to help protect your vitamin D levels.