A new study led by researchers from the University of Bath, the University of Cambridge, and the University of Birmingham shows that regular indoor exercise can blunt the winter drop in vitamin D. The findings offer a practical alternative to supplements for maintaining bone, muscle, and immune health during months with limited sun exposure, with relevance for global readers and Thai audiences alike.
Vitamin D, often called the “sunshine vitamin,” is essential for bone and muscle strength and immune function. In the United Kingdom, more than 10% of adults are believed to have insufficient vitamin D. In Thailand, research indicates that between 34% and 77% of adults experience deficiency or insufficiency, despite the country’s tropical climate. Urban living, sun avoidance, and air pollution contribute to low levels, making these results particularly meaningful for Thailand.
The UK study, published in May 2025, followed over 50 adults who were overweight or obese. They completed a 10-week indoor exercise program during winter, when sun-driven vitamin D synthesis is minimal. The regime included four weekly sessions: two treadmill walks, a longer steady-pace bike ride, and a high-intensity cycling interval. Those who exercised saw only a 15% winter decline in vitamin D, versus a 25% drop among non-exercisers. Crucially, the bioactive form of vitamin D remained intact in exercisers, supporting bone, muscle, and immune health. These results come from researchers at a leading UK university.
The lead researcher emphasized that this is the first study to show exercise alone can shield against the winter dip in vitamin D. Regular activity not only helps maintain vitamin D but also delivers broader health benefits that supplements cannot fully provide. Exercise appears especially beneficial for individuals who are overweight or obese, for whom supplementation often offers limited advantages.
Thai relevance is clear. Despite abundant sunlight, Thailand faces a substantial rate of suboptimal vitamin D levels. Thailand’s health data show significant portions of the population with deficiency or insufficiency, especially among city dwellers and the elderly. Factors include skin-lightening practices, indoor work and study, air pollution that blocks UVB rays, and limited consumption of vitamin D-rich foods such as fish, eggs, or fortified dairy.
Thai public health authorities and experts stress the importance of awareness about vitamin D status, particularly for vulnerable groups. The national recommended daily intake for adults is 15 micrograms, but achieving this target is challenging in practice.
Thailand’s rapid urbanization over the past decade, along with traditional preferences for fair skin, has contributed to a pervasive vitamin D deficiency that affects both rural and urban populations. The new research offers a practical approach: structured indoor exercise to maintain vitamin D status year-round, potentially reducing risks of osteoporosis, muscle weakness, respiratory infections, and related chronic diseases.
Looking ahead, the implications for Thailand are significant as the population ages and non-communicable diseases rise. A 2025 systematic review aligns with this view, showing that optimal vitamin D levels lower the risk of falls, fractures, and muscle injuries. Public health campaigns can incorporate these insights by promoting regular physical activity as a protective measure for vitamin D status, especially in the rainy season or for urban residents facing pollution and limited sun.
For individuals in Thailand, a simple takeaway emerges: aim for at least four sessions of moderate-to-vigorous exercise weekly, including indoor walking, stationary cycling, or group aerobics. Tailor routines to health status, and consider monitoring vitamin D levels and incorporating foods rich in vitamin D or fortified alternatives.
Public institutions and workplaces may find it beneficial to promote group exercise programs to help people maintain vitamin D health and overall well-being. This research reinforces the broader value of regular exercise for physical and metabolic health, including maintaining essential nutrients like vitamin D.
Notes for readers: This article integrates findings from international research with Thai health contexts. Data from reputable institutions in the UK and Thailand informs practical, culturally relevant guidance for staying healthy through the winter and beyond.