Take supplements? This simple lifestyle habit keeps vitamin D levels topped up in autumn - and costs nothing

We’ve reached the time of year when we can see multiple types of weather in one day, and the daylight hours are getting shorter. While nothing beats going outside in the sun to boost vitamin D levels, it can be difficult when sunny days are few and far between.

Taking tablets and eating foods rich in vitamin D can help, but with an estimated one in six of us deficient in the important vitamin, according to a government review, we may need a little more help.

A study, published in Advanced Science, may have the answer, as researchers found that those who exercise experience less of a drop in vitamin D levels from summer to winter compared to those who don't exercise at all.

Researchers from the universities of Bath, Cambridge, and Birmingham reviewed 50 overweight and obese participants who exercised indoors as part of a 10-week study from April to October, when vitamin D levels tend to fall due to a lack of sunlight. The exercise programme involved four sessions a week (two treadmill workouts, one longer static bike ride and one high-intensity interval bike session) while some participants did no exercise at all.

The group of participants who exercised experienced a 15% drop in vitamin D levels. This was 10% less than those who didn't exercise, who experienced a 25% drop.

One key aspect is that participants’ weight levels were kept stable throughout, so the researchers could attribute the results to exercise rather than weight loss. They also did not take supplements to ensure accurate results.

The study found that exercise preserved the body’s active form of vitamin D (1,25(OH)₂D₃), which supports bone health, the immune system, and our organs. Other studies have shown that taking vitamin D supplements alone doesn’t help maintain this active form.

Why does exercise help maintain vitamin D levels?

Exercise increases the concentration of vitamin D molecules every time you're active, explains Professor Dylan Thompson from the University of Bath. "And on top of this, doing regular activity helps to maintain your basal resting levels of vitamin D in winter. This means exercise gives you a double benefit to your vitamin D - firstly in and around each exercise bout, and secondly through your changing baseline levels," he said.

It's for this reason that the study is so important, adds lead author Dr Oly Perkin, from the Centre for Nutrition, Exercise and Metabolism, Department for Health at the University of Bath. He 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.”

To replicate the participant's 10-week study, you could walk briskly every day outdoors, which is free to do. Alternatively, if you have a bike, you could go for a bike ride. For those with a gym membership, taking up an indoor walking workout or spin class could be a good option.

How much vitamin D do we need in winter?

The National Institutes of Health recommends that adult women under 70 need 600IU of vitamin D daily, rising to 800IU after 70 years of age. The NHS suggests 10mg or 400IU.

However, to get the most from any source of vitamin D, many doctors recommend combining it with magnesium. Woman&home's resident GP, Dr Amir Khan, said we "need magnesium as it "activates the vitamin D". "It turns it from its inactive form to an active form so it can do all of its jobs", he said in a social media post last year.

Too much vitamin D can have the opposite effect and cause nasty side effects like fatigue, constipation, and issues with calcium absorption.

If you have any concerns, speak to your GP, who will be able to offer advice for your individual needs.