As winter rapidly approaches, the days will become shorter and darker, which has a significant impact on our vitamin D levels.

A lack of vitamin D has been associated with a wide range of negative health effects.

Many health professionals recommend taking vitamin D supplements this time of year, but why do we need them?

Why does our levels of vitamin D drop at this time of year?

“Sunshine is the main source of vitamin D – as our body creates vitamin D from direct sunlight on our skin,” explains Dr Angela Rai, GP at The London General Practice. “It is produced in the body when ultraviolet rays from sunlight pass through the skin and trigger vitamin D synthesis.”

However, the sun’s rays are less intense this time of year, so our levels drop.

“We also spend more time indoors and the days are shorter,” notes GP Dr Nisa Aslam from the Health and Food Supplements Information Service. “This means that less vitamin D is made in the skin through the autumn, winter and early spring.”

Why is vitamin D important for our health? 

“Vitamin D helps the body to absorb calcium and use phosphorus, which are essential for strong bones and teeth,” says Aslam. “Vitamin D is also important for the health and growth of our muscles.

“Plus, vitamin D is important for blood clotting and the immune system.”

Vitamin D has also been linked to protection against respiratory tract infections including Covid-19.

“A 2024 study undertaken by a team of Italian clinicians reported that vitamin D supplementation reduced the risk of Covid infections by 60%,” says Aslam. “Vitamin D in doses of 10-25 micrograms for 12 months has been associated with reduced risk of acute respiratory tract infection overall.”

Other research suggests that vitamin D could also help with dementia.

“Taking vitamin D supplements may help ward off dementia,” adds Aslam. “Researchers who worked on a 2023 study found that taking vitamin D was associated with living dementia-free for longer, and they also found 40% fewer dementia diagnoses in the group who took supplements.”

What are the signs you might have a vitamin D deficiency?

“Most people with a vitamin D deficiency don’t have any symptoms, or only have vague ones like tiredness or aches,” says Dr Elise Dallas, GP at The London General Practice. “But some signs of vitamin D deficiency include bone pain, muscle weakness (especially in the upper arms or thighs), depression or feelings of sadness, fatigue, sleeping issues and hair loss.

“Pale skin, loss of appetite and getting sick more easily can also be symptoms of vitamin D deficiency.”

However, these symptoms can be subtle and are easily attributed to other causes.

“They can also indicate various health issues, not just vitamin D deficiency,” says Dr Matthew Calcasola, GP and chief medical officer at Get A Drip. “If you’re experiencing these symptoms persistently, especially during winter months or if you have limited sun exposure, it’s advisable to consult with a healthcare professional.

“A simple blood test can accurately determine your vitamin D levels.”

What age demographics are more likely to have a vitamin D deficiency?

“Older people aged 65 and over, and young children under five are more likely to have a vitamin D deficiency,” says Calcasola. “For older adults, your skin doesn’t make vitamin D when exposed to sunlight as efficiently as when you’re younger.

“Children are more susceptible as their bodies are still developing, and they are exposed less to sunlight for safety reasons.

“However, especially during wintertime, vitamin D deficiencies among healthy, young adults are common due to shorter, darker days.”

How else can you top up your levels?

The lack of sunlight during the colder months means we should seek alternative sources of vitamin D this time of year.

The NHS recommends that everyone (including pregnant and breastfeeding women) should consider taking a daily supplement containing 10 micrograms of vitamin D during the autumn and winter.

“Vitamin D is in very few foods (e.g, oily fish, egg yolks, fortified margarine) and few people can top up levels adequately with diet,” explains Aslam. “As it takes time and effort to get our diets back on track, I suggest that people top up with a daily multivitamin and multi-mineral supplement containing vitamin D.”

You can also raise your vitamin D levels through booster shots.

“Booster shots can provide a quick and efficient way to raise vitamin D levels in the body – especially for those who have difficulty absorbing vitamin D through oral supplements or dietary sources,” says Calcasola. “They are administered only by registered healthcare professionals and can help replenish vitamin D stores to support overall health and wellbeing.”