The subtle signs of a vitamin D deficiency – and how to get enough this autumn

With winter fast approaching, your body might be suffering more than you realise.

Direct sunlight on the skin is essential for producing vitamin D, which plays a crucial role in supporting bone, muscle and immune health. However, solar strength during this time of the year is insufficient to fulfil this process.

A shortage of vitamin D can lead to numerous subtle health issues that may remain hidden for a long time, though specialists emphasise that optimal levels allow the body to operate far more efficiently.

“You can get most vitamins within a balanced diet, so if you’re having lots of good veg, fruit, etc, you can get the majority of your vitamins,” Dr Henrik Premasundaram, a GP and health screener at HCA Healthcare UK, tells the Press Association.

“But with vitamin D you simply can’t, because the main production is from the sun. Vitamin D is essential for healthy bones, muscles, and normal immune function, and if you’re deficient, it can lead to things like tiredness, and in really low cases it can affect your mood.”

As Bridget Benelam, a nutrition scientist from the British Nutrition Foundation (BNF), explains: “Vitamin D is unique among the essential vitamins because our main source is from sunlight, not the foods and drinks we consume. Sunlight on our skin triggers a vital chemical reaction, allowing the body to produce vitamin D.

“During the summer, short periods of sunlight exposure are enough for most people to make vitamin D. But in the UK from October to March the sunlight isn’t strong enough to make vitamin D, and the body relies on stores built up during the summer and on dietary sources of vitamin D.”

She says if the body is lacking in the vitamin there may be effects that people don’t realise are linked to vitamin deficiency.

“Vitamin D deficiency doesn’t always cause obvious symptoms straight away,” she points out. “But low levels over time can lead to bone pain, muscle weakness and an increased risk of falls in older adults.”

In children, severe deficiency can result in rickets, while in adults it can cause osteomalacia, a condition that leads to soft, weak bones.

In addition, a 2023 study by the universities of Exeter and Calgary of more than 12,000 people, some of whom took vitamin D supplements and some who didn’t, found 40 per cent fewer dementia diagnoses in the supplement-taking group.

But what’s the best way of getting enough vitamin D, particularly in the dark and dreary UK winter?

The exact amount of sunlight needed to get enough vitamin D varies, says Benelam, depending on factors such as skin type, age, clothing and weather conditions.

Premasundaram says: “Most people can maintain their vitamin D levels through sunlight, especially during the spring and summer, but definitely not through the autumn and winter, just because of the way the UVB rays come through in the UK – they’re essentially just too low because of either the clouds or the sun exposure.

“Even on a sunny day in the UK autumn and winter you just won’t get enough vitamin D from the sun.”

And he points out getting sunlight just on your face is unlikely to produce the required amount of vitamin D.

“It’s not necessarily just sunlight on your face that’s enough,” he explains. “You actually need a bigger surface area, so it’s quite hard to get the amount you really need simply from sun exposure.”

It is possible to get some vitamin D from your diet, but you’re unlikely to be able to get enough, and because so little can be produced through sunlight on the skin in the UK autumn and winter, vitamin D supplementation is advised for both adults and children.

Benelam says: “There aren’t many good sources of vitamin D in the diet – oily fish such as salmon, mackerel and sardines provide the most, and you can also get vitamin D from eggs, fortified cereals and fat spreads, plus vitamin D-enriched mushrooms.”

She says a 140g portion of baked salmon provides about 10 micrograms of vitamin D (the recommended daily amount), a 30g portion of fortified cereal about 1.4 micrograms, one egg provides about 1.6 micrograms and an 80g portion of enriched mushrooms 3.2 micrograms.

“While it’s possible to get some vitamin D from food, it can be difficult to achieve the recommended intake through diet alone,” she explains, “because relatively few foods naturally contain significant amounts.”

Premasundaram adds: “It’s really, really hard to get enough vitamin D from diet alone, so in the winter months we’d encourage people to take a supplement – it’s just an easy way of getting your daily vitamin D requirement. It’s important.”

Benelam says the Government recommends a daily 10 microgram vitamin D supplement for everyone aged over five years from October to March. The NHS also recommends supplements for babies and young children, with suitable amounts depending on whether babies are breastfed or bottle fed, and on the age of the child.

Benelam points out that people with darker skin, those who cover their skin for religious or cultural reasons, and those who don’t get outside regularly, are at higher risk of vitamin D deficiency, so it’s recommended that they take a vitamin D supplement all-year round.

The National Diet and Nutrition Survey measures levels of vitamin D in blood, and the latest results show nearly one-in-five adults (18 per cent) are vitamin D deficient.

But Benelam says that despite this, BNF surveys suggest only around half of people are aware of the recommendation to take a vitamin D supplement during the autumn and winter months.

“A daily 10 microgram supplement is a simple and inexpensive way to help maintain adequate vitamin D levels when sunlight exposure is limited,” she stresses.

But if people do start taking vitamin D supplements, are they likely to notice a difference in how they feel?

“Yes, definitely,” stresses Premasundaram. “It can even help with moods, and help people feel more energetic.

“I take vitamin D regularly, and I feel a lot better – I feel less tired. Is it a placebo? Maybe a small percentage of that, but I think it definitely has a good impact on patients’ wellbeing.”