Exercise helps maintain vitamin D levels in winter without supplements
Researchers found that overweight and obese adults who completed a 10-week indoor exercise programme over winter experienced significantly smaller drops in vitamin D levels compared with those who did not exercise, even though their body weight was deliberately maintained.
More than 50 people took part in four sessions per week of two treadmill walks, one longer steady-state bike ride, and one high-intensity interval bike session.
Exercise completely preserved the body's active form of vitamin D, which plays a key role in supporting bone health, the immune system, and various organs.
Previous studies suggest that vitamin D supplements alone do not help maintain this active form.
The small-scale study was led by academics from the University of Bath, University of Birmingham and University of Cambridge.
Lead author Dr Oly Perkin, from the University of Bath, said: 'This is the first study to show that exercise alone can protect against the winter dip in vitamin D.
'It's a powerful reminder that we still have lots to learn about how exercise benefits our health.'
People who exercised saw a smaller drop in their overall vitamin D levels over winter of around 15%, compared with a 25% drop in those who did not exercise.
Those who exercised kept healthy levels of the active form of vitamin D, which helps support the immune system and bone health.
In the non-exercising group, levels of this active form fell by 15%.
Weight was kept stable throughout the study, proving the effect was due to exercise, not weight loss.
To ensure sunlight did not skew results, the study ran between October and April – when natural vitamin D production from sunlight is minimal in this part of the UK – and participants were asked to avoid supplements.
A previous study from the team showed that a single workout can briefly boost vitamin D levels, but this is the first to show that regular cardio exercise can maintain basal circulating vitamin D levels and offer lasting protection during the winter months.
Principal investigator Professor Dylan Thompson, from the University of Bath, said: 'Collectively, the findings from the VitaDEx project show that exercise increases the concentrations of vitamin D metabolites each time you are active and, on top of this, doing regular activity helps to maintain your basal resting levels of vitamin D during winter.
'This means exercise gives you a double benefit to your vitamin D, first in and around each exercise bout, and second through changing your baseline levels.'
The study offers compelling evidence that exercise could be an effective winter vitamin D strategy, especially for those who are overweight or obese for whom vitamin D supplements are less effective.
Liam Kilawee, who took part in the study, said: 'I was impressed on how thorough the process was and how the team engaged with me during research period.
'The results were pleasing as I could see that my actions had a positive reaction.'
– The study, Exercise without Weight Loss Prevents Seasonal Decline in Vitamin D Metabolites: The VitaDEx Randomised Controlled Trial, is published in the journal Advanced Science.
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