Some time around November you notice it. You’re flat by mid-afternoon, it takes you longer to get going in the morning, and the sofa feels like the obvious place to spend the evening. It’s tempting to blame your age. Lately, a lot of people have started blaming vitamin D instead.
That isn’t a daft idea. Britain is a poor place to make vitamin D for half the year, and plenty of us run low by spring. A cheap supplement won’t fix every kind of tiredness, though, and the evidence on energy levels is weaker than the marketing suggests. Here’s what’s known, what isn’t, and what’s worth doing.
Why does Britain leave you short of vitamin D?
Most of your vitamin D doesn’t come from food. Your skin makes it when it’s exposed to sunlight. In the UK, NHS guidance says most people make enough from late March or April to the end of September, as long as they get outside regularly and eat a reasonably balanced diet.
From October to March the sun is too low in the sky for your skin to make much at all, however long you spend out in the cold. Food helps a little but rarely closes the gap. The main sources are oily fish such as salmon, mackerel, sardines and herring, along with red meat, liver, egg yolks and fortified foods such as some breakfast cereals and fat spreads. Few people eat enough of them to cover a whole winter.
Midlife makes things a bit harder. If you commute in the dark, work indoors, spend weekends in the car or garage, or carry extra weight, you’re likely to have less vitamin D to begin with. Older skin also makes it less efficiently than younger skin.
What the NHS actually recommends
The advice is short and it is the same across the UK. NHS guidance in England, the Scottish Government’s advice and the matching advice in Wales and Northern Ireland all say adults should consider taking 10 micrograms of vitamin D a day during autumn and winter, roughly October to March. Ten micrograms is the same as 400 international units (IU), which is the figure you’ll often see on the label.
Some people are advised to take it all year round. That includes people who rarely get outdoors, people living in care homes, people who usually cover most of their skin when outside, and people with darker skin, such as those of African, African-Caribbean or South Asian heritage, who may not make enough even in summer.
You generally buy it yourself from a pharmacy or supermarket, where a basic daily supplement usually costs a few pounds for several months’ supply. NHS guidance in Scotland says plainly that supplements for general prevention should be bought over the counter, not prescribed.
Vitamin D is cheap insurance for your bones and muscles through a British winter. It is not a substitute for finding out why you’re exhausted.
Can low vitamin D make you tired?
Here the honest answer is less satisfying. A long-term lack of vitamin D is well known to cause bone pain, muscle weakness and, in adults, a softening of the bones called osteomalacia. Aching muscles and weak legs can certainly feel like being worn out.
The evidence that taking vitamin D gives you more energy, when you aren’t actually deficient, is weak and mixed. Some small studies point to a benefit in people who start with very low levels. Larger trials have generally been disappointing for broader claims, including the hope that supplements might prevent heart disease or cancer in people who already have enough.
In practice, taking the recommended 10 micrograms over winter is sensible, low-risk advice. Expecting it to bring back the energy you had at 35 is likely to end in disappointment.
More isn’t better, either. Vitamin D is stored in the body, and very high doses over a long time can push calcium levels up, which can harm your kidneys, bones and heart. NHS guidance says adults should not take more than 100 micrograms (4,000 IU) a day unless a doctor has advised it. Some high-strength products sold online go well beyond what you need, so read the label. If you take other medicines or have kidney problems, ask your pharmacist before you add a supplement.
Should you get your vitamin D levels tested?
For most men the answer is no, or not as a first step. The NHS doesn’t routinely test vitamin D in people without symptoms, because the standard advice is simply to take the winter supplement. Private finger-prick tests are widely available, but on their own they rarely change what you should do.
A GP may check your level if there’s a clinical reason, such as bone pain, unexplained muscle weakness, a fracture after a minor fall, or a condition or medicine that affects how you absorb vitamin D. If a deficiency is confirmed, treatment is usually a higher dose for a set period, and your GP will decide on that. Don’t try to work out a treatment dose yourself.
When tiredness needs more than a supplement
Persistent tiredness has plenty of possible causes, and vitamin D is far from the most likely culprit. NHS guidance lists several conditions worth ruling out. Iron deficiency anaemia often comes with breathlessness, palpitations and pale skin. Diabetes can show up as tiredness plus thirst, weight loss and getting up at night to pee. An overactive or underactive thyroid can also leave you drained. Low vitamin B12 or folate, poor sleep, sleep apnoea, depression, too much alcohol and some medicines can all play a part as well.
If you’ve felt tired most of the time for several weeks and sleeping more, cutting back on alcohol and moving a bit more haven’t helped, book a GP appointment. They may suggest blood tests, which commonly check for anaemia, diabetes and thyroid problems. If you’re in England and aged 40 to 74 without an existing heart or kidney condition, your free NHS Health Check every five years is another chance to look at your blood sugar, cholesterol and blood pressure. Scotland, Wales and Northern Ireland don’t offer the same scheme, so speak to your GP practice there.
Don’t wait for a routine appointment if tiredness comes with unexplained weight loss, a lump or swelling, or blood in your pee or poo. Call NHS 111 if you feel unwell and aren’t sure what to do. Call 999 for chest pain, severe breathlessness or sudden weakness.
In short
Low vitamin D is common in UK winters, and across the UK adults are advised to consider 10 micrograms a day from October to March, or all year if they rarely get outside or have darker skin. It’s cheap and sensible for your bones and muscles, but don’t go above 100 micrograms a day unless a doctor tells you to. The evidence that it boosts energy is weak, so if you’ve been tired for weeks, see your GP rather than relying on a supplement.
Sources
Midcent Health
Adrian Irving writes about health for men 45 and over who would rather do something than worry. Training, weight loss, sleep, cholesterol and blood tests, heart health, testosterone, the prostate, mental health and your sex life – what the evidence says, what's worth trying, and when it's time to see your GP.
One of Midcent's writers. Spotted something? Write to adrian@midcent.uk.
