Regular exercise can prevent a steep winter decline in vitamin D levels, offering an alternative to supplements, according to a new study led by researchers from the University of Bath, University of Cambridge, and University of Birmingham. The findings, relevant for both global audiences and Thailand, provide practical advice for maintaining musculoskeletal and immune health during months with limited sunlight, when the risk of vitamin D deficiency sharply increases (BBC).
Vitamin D, sometimes called the “sunshine vitamin”, is crucial for bone, muscle, and immune health. Yet, more than one in 10 adults in the UK are thought to lack sufficient vitamin D, while studies in Thailand have found that between 34% and 77% of adults face deficiency or insufficiency, despite the nation’s tropical climate (ScienceDirect, PMC). Urban lifestyles, sun avoidance, and air pollution contribute to widespread low levels, making these new findings highly relevant for Thai readers.
The UK-based study, published in May 2025, involved over 50 overweight and obese adults who participated in a 10-week indoor exercise program over winter, a time when vitamin D synthesis from sunlight is minimal. Exercise routines included four weekly sessions: two treadmill walks, a longer steady-state bicycle ride, and a high-intensity interval cycling session. Results showed that those who exercised experienced only a 15% reduction in their vitamin D levels over winter, compared to a 25% drop in non-exercisers. Most notably, exercise completely preserved the bioactive form of vitamin D necessary for bone and muscle health, as well as immune function (University of Bath, ScienceDaily).
Lead researcher from the University of Bath stated, “This is the first study to show that exercise alone can protect against the winter dip in vitamin D.” The researcher emphasized that regular activity not only helps maintain vitamin D but delivers health benefits beyond what supplements can offer: “If you’re worried about your vitamin D levels in the winter, keeping up regular exercise every week will help, and offer a load of health benefits that vitamin D supplements cannot. It’s a powerful reminder that we still have lots to learn about how exercise benefits our health.” Another co-author noted that, “exercise gives you a double benefit to your vitamin D,” highlighting the unique efficacy for individuals who are overweight or obese, for whom supplements are often less effective.
For Thailand, these findings resonate strongly. Despite abundant sunlight, a 2019 review of Thailand’s 4th National Health Examination Survey showed about 45% of adults had suboptimal vitamin D levels, with 7% classified as deficient (PubMed). Thai dermatologists and city dwellers, in particular, report even higher rates of deficiency, underscoring the complexity of the problem (PubMed). Factors include preference for lighter skin leading to sun avoidance, increasing time indoors for work or study, air pollution blocking UVB rays, and low consumption of vitamin D-rich foods such as fish, eggs, or fortified dairy.
Nationwide concern has led the Thai Ministry of Public Health and academic experts to advocate for increased awareness of vitamin D status, especially among vulnerable groups like the elderly, urbanites, and people with obesity. The Thai Food and Drug Administration’s Recommended Daily Intake (RDI) for vitamin D stands at 15 micrograms for adults (Siam Development), but meeting this threshold is often difficult in practice.
Historical context further illuminates the issue. Although Thailand is a tropical country, the past decade’s rapid urbanization has reshaped lifestyles. Traditions prioritizing fair skin have deep roots, with many Thai people preferring to cover up outdoors or use umbrellas to avoid tanning. These cultural tendencies, while longstanding, have unexpectedly contributed to a hidden epidemic of vitamin D deficiency, documented in both rural and urban populations (PMC).
In light of this, the new research offers a practical, culturally-sensitive solution for Thais reluctant to seek sun exposure. Structured indoor exercise can help maintain healthy vitamin D status year-round, reducing risk of osteoporosis, muscle weakness, respiratory infections, and even certain chronic diseases linked to deficiency (MedicalXpress).
The importance of these findings extends into the future. As Thailand’s population ages and the prevalence of non-communicable diseases such as diabetes and cardiovascular disease rises, strategies that strengthen musculoskeletal and immune health will be increasingly crucial. A recent 2025 systematic review confirmed that optimal vitamin D levels lower the risk of falls, fractures, and muscle injuries — issues already straining Thailand’s healthcare system (PubMed).
For Thai readers, the takeaway is clear: making time for moderate-to-vigorous exercise each week, even indoors, can play a vital role in maintaining vitamin D levels and overall health. This is especially important in periods of reduced sunlight, such as the rainy season or for those living in polluted urban centers. Simple routines combining walking, cycling, and high-intensity intervals — tailored to individual health status — are both accessible and effective. For those at higher risk, such as older adults or people with obesity, combining exercise with regular vitamin D monitoring and a diet rich in natural or fortified sources is advisable.
Public health campaigns may wish to incorporate these research findings into their messaging, encouraging physical activity not only for fitness or weight management but as an effective safeguard against vitamin D deficiency. Educational institutions and workplaces could also facilitate group exercise programs, making it easier for people to reap these health benefits.
Ultimately, this research highlights a broader theme relevant to Thailand and beyond: the multifaceted value of regular exercise for physical and metabolic wellbeing, including the maintenance of essential nutrients like vitamin D.
For Thais looking to protect their health, the recommendation is straightforward: incorporate at least four sessions of moderate-to-vigorous exercise, such as indoor walking, stationary cycling, or aerobic classes, into your weekly routine. This simple lifestyle adaptation can help ensure your body has the vitamin D it needs to grow strong bones, muscles, and a resilient immune system—regardless of the season or the sky outside.