Vitamin D deficiency is remarkably common in the UK - and remarkably easy to miss. Unlike a cold or a pulled muscle, low vitamin D rarely announces itself. Its symptoms are vague, slow-building, and easy to blame on stress, poor sleep, or simply "winter." That's exactly why it's worth knowing what to look for.
And the timing matters: autumn is now here. The clocks will soon go back, the days are getting shorter, and from October onwards the UK sun no longer provides the UVB your skin needs to make vitamin D. Whatever levels you've built up over summer will steadily drain over the coming months which makes right now the ideal time to start thinking about your vitamin D, before any shortfall shows up as the symptoms below.
In this article, we'll cover the most common signs of low vitamin D, why deficiency is so widespread in the UK, and what to do if you suspect your levels are low.
Why is vitamin D deficiency so common in the UK?
Vitamin D is unusual among nutrients: your body makes most of it itself, in the skin, when exposed to UVB rays from sunlight. The problem? Between roughly October and March, the sun in the UK sits too low in the sky for meaningful UVB to reach us - no matter how sunny the day looks.
Add in office jobs, long commutes, sunscreen use, and the fact that very few foods contain significant vitamin D, and it's easy to see why so many people in the UK run low over winter. Government surveys have consistently found that a significant proportion of UK adults have low vitamin D status by late winter, which is why the NHS advises that everyone consider a daily supplement between October and early March.
Some groups are at higher risk year-round, including people with darker skin tones (melanin reduces vitamin D synthesis), those who spend little time outdoors, people who cover their skin when outside, older adults, and anyone living in the northern parts of the UK.
Common signs your vitamin D might be low
An important caveat before we start: none of these symptoms is unique to vitamin D deficiency. Each can have many other causes, which is why testing - not self-diagnosis - is the only way to know for sure. But if several of these sound familiar, particularly in winter, it may be worth investigating.
1. Persistent tiredness and fatigue
One of the most commonly reported signs of low vitamin D is a lingering, hard-to-shake tiredness - the kind where you sleep a full night and still feel drained. Because fatigue has so many possible causes, it's often the last thing people connect to a vitamin. But vitamin D receptors are found in tissues throughout the body, and low levels have been repeatedly associated with reduced energy and daytime tiredness in research.
2. Frequent colds and infections
Vitamin D contributes to the normal function of the immune system. Some people who are run down with one bug after another through the winter months - while others around them stay well - turn out to have low vitamin D on testing. If your immune system seems to struggle every winter, your vitamin D status is one sensible thing to check.
3. Aching bones and lower back pain
Vitamin D plays a central role in calcium absorption and the maintenance of normal bones. When levels are very low for a long time, bones can become less well mineralised, which may show up as a dull ache - commonly in the lower back, hips, or legs. In severe, prolonged deficiency this can develop into osteomalacia (softening of the bones) in adults, a condition that was thought to be consigned to history but still appears in UK clinics.
4. Muscle weakness, aches, or cramps
Vitamin D contributes to normal muscle function, and muscle pain or weakness is a recognised feature of significant deficiency. Some people describe heaviness in the legs, difficulty climbing stairs, or general muscle aches with no obvious cause. Athletes and gym-goers sometimes notice it as a plateau in performance or slower recovery.
5. Low mood, particularly in winter
Many people report their mood dips in the darker months, and researchers have observed associations between low vitamin D levels and low mood. It's important to be clear about what the science does and doesn't say: an association is not proof that one causes the other, and vitamin D is not a treatment for depression or seasonal affective disorder. If low mood is affecting your life, speak to your GP. But given how common winter deficiency is in the UK, maintaining healthy vitamin D levels is a reasonable part of looking after yourself through the season.
6. Slow wound healing
Some research suggests that people with low vitamin D levels may experience slower healing of cuts, scrapes, and post-surgical wounds. If minor injuries seem to take longer to heal than they used to, it's one more data point worth mentioning to your GP.
7. Hair thinning
The evidence here is less established than for bones and muscles, but low vitamin D has been observed in some people experiencing hair shedding or thinning. Hair loss has many causes - genetics, stress, thyroid issues, iron status - so this sign alone shouldn't send you to the supplement aisle. But it can be part of a bigger picture.
Who is most at risk?
You're statistically more likely to be low in vitamin D if you:
- Spend most daylight hours indoors (office workers, night-shift workers, gamers - we see you)
- Have darker skin, as melanin reduces the skin's ability to produce vitamin D from sunlight
- Cover most of your skin when outdoors
- Are over 65, as skin becomes less efficient at producing vitamin D with age
- Are pregnant or breastfeeding
- Live in Scotland or northern England, where winter UVB is even scarcer
- Follow a vegan or vegetarian diet, since the few natural food sources (oily fish, egg yolks) are animal-based
- Are carrying excess body weight, as vitamin D is fat-soluble and can be sequestered in fat tissue
How do you find out for sure?
The only reliable way to know your vitamin D status is a blood test measuring 25-hydroxyvitamin D - the storage form of the vitamin.
Through your GP: If you have symptoms or risk factors, your GP may arrange a test on the NHS. Testing isn't routine for everyone, so it helps to describe your symptoms and risk factors clearly.
Home testing: Several UK companies offer finger-prick vitamin D tests that are analysed in accredited labs, typically for £25–40. These can be a convenient option if you simply want to know where you stand.
In the UK, results are usually given in nmol/L. As a rough guide, below 25 nmol/L is considered deficient, 25–50 nmol/L is often described as insufficient, and above 50 nmol/L is generally considered adequate for most people. Your GP or the testing lab will interpret your specific result.
What to do if you're low
Follow NHS guidance on supplementation. The NHS recommends that adults and children over four consider a daily supplement of 10 micrograms (400 IU) during autumn and winter, and year-round for higher-risk groups. If a test shows you're significantly deficient, your GP may recommend a higher short-term dose to restore your levels - follow their advice rather than megadosing on your own, as it is possible to take too much vitamin D.
Choose D3 where possible. Vitamin D3 (cholecalciferol) is the form your skin naturally produces, and research suggests it raises blood levels more effectively than D2. Vegans should look for lichen-derived D3.
Take it with food. Vitamin D is fat-soluble, so it's better absorbed alongside a meal containing some fat.
Get sensible sun in summer. From around late March to September, short periods of midday sun exposure on bare forearms and lower legs - without burning - help your body build its own supply.
The bottom line
Vitamin D deficiency is one of the most common nutritional shortfalls in the UK, and its symptoms - fatigue, frequent infections, aching bones and muscles, low winter mood - are easy to dismiss as everyday life. With autumn already underway, now is the time to act: get your levels tested if several of these signs sound familiar, speak to your GP if symptoms are affecting you, and follow NHS guidance on daily supplementation through the darker months.
Your future, less-tired self will thank you.
Shop Focus Vitamin D3 & K2 here.
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