Dr. Joseph Mercola - Take Control of Your Health How Exercise Helps Maintain Healthy Vitamin D Levels in the Wintertime
Oct 11, 2025
Winter's weak sunlight can lead to vitamin D deficiency, especially for those with excess body fat. A study found that exercise alone helps maintain active vitamin D levels without supplements. Physical activity enhances enzyme activity in fat tissue, boosting the conversion of stored vitamin D. Those with more fat benefited the most from this activation. Recommendations include regular cardio and strength training to effectively manage vitamin D through winter. Additionally, testing vitamin D levels and proper supplementation with magnesium and K2 is advised.
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Winter Sunlight Can't Sustain Vitamin D
- In northern winters UVB is too weak to make vitamin D, raising deficiency risk.
- Excess body fat sequesters vitamin D, reducing its availability for activation by cells.
Exercise Preserves Active Vitamin D
- A 10-week winter trial showed only the exercise group maintained active vitamin D.
- Sedentary participants lost ~15% of their active form while exercisers held levels steady without fat loss.
Exercise Reprograms Fat Tissue Enzymes
- Exercise shifted fat-tissue enzyme activity toward activation and away from breakdown of vitamin D.
- Activation enzyme rose and deactivation fell, conserving the usable form during winter.