Winter Workouts Help Sustain Vitamin D Levels, New Study Shows

As daylight hours shrink and cold weather sets in, many people face a silent winter risk: declining vitamin D levels. Our primary source of vitamin D is through the skin and it needs to be from ultraviolet radiation (UVR) between 290 & 315 nanometres in wavelength (1). During winter, serum vitamin D levels naturally decrease because the angle of the earth in relation to the sun changes and we are exposed to less of these particular UVR lengths.

A 2015 study found that in Melbourne in the winter, most people were not able to achieve the recommended amount of sun exposure for maintaining adequate vitamin D levels (2). Furthermore, even when they did achieve this their levels were still low.

New research suggests there’s an effective solution that doesn’t involve supplements or a holiday up north - just movement. A first of its kind study has recently found that regular exercise during winter can reduce the usual seasonal drop in vitamin D (3).

The study was a randomised control trial conducted in the UK. It tracked a group of 51 overweight adults over a 10-week period during winter. Participants were randomly assigned to two groups: one engaged in regular aerobic exercise 4 times per week, while the other remained sedentary. Neither group took vitamin D supplements, and the exercise program was designed to not cause significant weight loss.

Excitingly, the exercising group maintained adequate levels of D₃ throughout the winter, whilst those that didn’t exercise resulted in a 25% decline. D3 is the active form of vitamin D in our bodies. Exercising participants also experienced a smaller drop in stored vitamin D levels when compared to those that didn’t exercise.

Exercise and Vitamin D: What’s the Link? 

The researchers use previous evidence to explain the link. Vitamin D is fat-soluble, meaning it is stored in fat tissue. In people who are overweight or obese, more vitamin D can become stored in fat, resulting in lower amounts available in the bloodstream. Furthermore, weight loss or intermittent fasting helps to maintain vitamin D levels. The general belief held by researchers is that exercise mobilises stored vitamin D from fat cells, releasing it into circulation. This theory aligns with the study’s findings: despite no weight loss, participants who exercised maintained healthier vitamin D levels than their sedentary counterparts.

Why does Vitamin D Matter? 

Beyond growing bones, vitamin D has been associated reducing the risk of heart disease, cancer, COVID-19, stroke, chronic lower respiratory diseases, Alzheimer’s disease and other dementias, diabetes mellitus, and kidney disease (4).

Effective vitamin D supplementation may need to be done with exercise:

The researchers point out that taking vitamin D supplements usually doesn't have much effect on the active form of vitamin D in the body (called 1,25(OH)2D), unless you're also getting a lot of exercise such as military recruits or athletes. Additionally, people who are overweight may not see the same boost in vitamin D levels from supplements as those with normal weight. Even when vitamin D levels in the blood improve through supplementation, other potential benefits such as stronger muscles or a reduced risk of cancer doesn't always happen. In short, exercise seems to play a key role in how the body uses vitamin D, and it doesn’t work the same way as just taking supplements.

Stay active this winter!

This study delivers a powerful message: that you don’t need to lose weight or rely on supplements to protect your vitamin D status during the colder months. Simply get moving! Moderate intensity activity such as walking, cycling, or dancing a few times a week may help keep your vitamin D levels more stable and support your overall health. Winter exercise also boosts energy, improves mood, and enhances cardiovascular fitness, making it an all-around win.

If you’ve been tempted to hibernate this winter, this study offers a compelling reason to stay active. Even without weight loss, exercise can help you maintain vitamin D levels and support your bone health, immune system, mood, and muscles. It’s not just about fitness; it’s a simple, effective way to thrive during winter.

References: 

1. Wacker M, Holick MF. Sunlight and Vitamin D: A global perspective for health: A global perspective for health. Dermatoendocrinol [Internet]. 2013;5(1):51–108. Available from: http://dx.doi.org/10.4161/derm.24494 

2. Kimlin M, Brodie A. A study of UV and vitamin D in Melbourne adults: Research summary [Internet]. Melbourne: Vic Health; 2015. Available from: https://www.vichealth.vic.gov.au/sites/default/files/UV-and-vitamin-D_research-summary_260315.pdf#page=3.18 

3. Perkin OJ, Davies SE, Hewison M, Jones KS, Gonzalez JT, Betts JA, et al. Exercise without weight loss prevents seasonal decline in vitamin D metabolites: The VitaDEx randomized controlled trial. Adv Sci (Weinh) [Internet]. 2025;e2416312. Available from: http://dx.doi.org/10.1002/advs.202416312 

4. Grant WB, Wimalawansa SJ, Pludowski P, Cheng RZ. Vitamin D: Evidence-based health benefits and recommendations for population guidelines. Nutrients [Internet]. 2025;17(2):277. Available from: http://dx.doi.org/10.3390/nu17020277