When the British summer finally arrives and the sun comes out, most of us assume we can put our bottle of vitamin D back in the cupboard until winter.
It seems completely logical that spending a few hours outside in the sunshine should automatically top up your nutrient levels, but the reality of how our bodies make vitamin D is a bit more complicated. Between spending the vast majority of our working hours stuck inside an office, slathering on necessary sun cream that blocks out UV rays, and dealing with the standard overcast British weather, a lot of us still fail to get what we need even in July.
Relying entirely on summer sun to fix a deep-seated deficiency usually backfires, leaving your immune system and bone health completely unprotected. If you want to keep your energy levels steady year-round, keeping up with a daily supplement is a smart habit that you shouldn’t just drop the moment the temperature rises.
The sun alone isn’t enough for a lot of people.
Getting enough vitamin D from sunlight requires around five to 30 minutes of direct sun exposure a day, and that rises to around twenty-five minutes for people with darker skin tones, whose skin needs more sunlight to produce the same amount. For anyone working indoors all day, studying, caring for someone at home, or simply not getting outside regularly, hitting that threshold consistently just isn’t realistic even in summer. Studies suggest that nearly half of UK adults have below-optimal vitamin D levels, and perhaps most surprisingly, adults aged 18 to 29 have the lowest average of any age group.
The assumption that young, otherwise healthy people are fine tends to mask how sedentary and indoor-heavy modern life actually is. A student sitting through lectures and studying in their room, or someone commuting and spending the day at a desk, isn’t getting meaningfully more sun in June than they were in January. The season changes, but the daily routine often doesn’t.
Certain groups are advised to supplement all year, not just in winter.
The NHS recommends that all children aged one to four and all babies under twelve months take a daily vitamin D supplement throughout the entire year, not just during the darker months. The same applies to people who are housebound or living in care homes, those who wear clothing that covers most of their skin when outdoors, and people with darker skin tones. For these groups, summer sunshine doesn’t change the picture enough to make supplementation unnecessary.
This is worth knowing because the standard advice around vitamin D tends to focus on October through to early March as the key supplementation window for the general population. That’s accurate for many people, but it can give the impression that everyone is covered once spring arrives, which isn’t the case for the groups above or for anyone whose lifestyle limits their outdoor time regardless of the season.
There’s an important difference between deficiency and just being below optimal.
Vitamin D deficiency, defined as a blood level below 25 nmol/L, is a medical matter that should be addressed with a doctor rather than self-managed with an over-the-counter supplement. Being insufficient, which falls between 25 and 50 nmol/L, is a separate category that’s common and worth addressing but doesn’t carry the same urgency. Adequate levels sit between 50 and 75 nmol/L, and optimal is considered anything above 75 nmol/L. Most people buying supplements off the shelf are likely somewhere in the insufficient range rather than genuinely deficient, but without a blood test, it’s impossible to know.
Getting a blood test is the only reliable way to find out where you actually stand, and it’s particularly worth doing if you get ill frequently or feel like your health isn’t quite where it should be. GPs can arrange this, and private testing is also widely available. Acting on guesswork rather than actual data means some people supplement unnecessarily, while others who genuinely need it assume they’re fine.
If you do supplement, vitamin D3 is the better choice.
Not all vitamin D supplements are the same. There are two main forms available: vitamin D2 and vitamin D3. Experts recommend D3 specifically because it appears to be more effective for immune function and is the form the body produces naturally through sun exposure. D2 is still used in some supplements and fortified foods, but D3 is the version most commonly recommended by nutritionists and is widely available in most pharmacies and health food shops.
The NHS recommended daily amount for healthy adults, including people who are pregnant or breastfeeding, is 10 micrograms per day, which is also written as 400 IU. For babies up to twelve months old, the recommendation is 8.5 to 10 micrograms daily, and for children aged one and over, it’s 10 micrograms. These are the amounts considered appropriate for maintaining adequate levels in people who aren’t deficient and don’t have a medical condition requiring higher doses.
Taking too much vitamin D is a real risk that doesn’t get talked about enough.
Vitamin D is a fat-soluble vitamin, which means the body stores rather than flushes out any excess, and taking too much over a long period of time can lead to a condition called hypercalcaemia, where calcium builds up to harmful levels in the blood. Symptoms can include nausea, weakness, frequent urination, and in serious cases, kidney damage. This isn’t something that happens from a few extra weeks of supplementing in spring, but it’s a legitimate concern for anyone taking high-dose supplements without medical supervision over an extended period.
The risk is worth flagging because vitamin D has had a lot of positive attention in recent years and some people assume that more is simply better. It isn’t. The NHS is clear that healthy people without a diagnosed deficiency should stick to the standard 10 microgram daily recommendation, rather than going above it without guidance from a doctor. If your levels are genuinely low, a GP can advise on whether a higher therapeutic dose is appropriate and for how long.
Spending time outside is still vital, even if you’re supplementing.
Sun exposure does more than just produce vitamin D. Time outdoors is linked to better sleep, improved mood, reduced stress levels, and lower blood pressure, none of which a supplement can replicate. Getting outside for even short periods during the middle of the day, when UV levels are high enough for vitamin D production, is worth building into a daily routine whether or not you’re also taking a supplement. Exposing your forearms and lower legs rather than just your face and hands makes a meaningful difference to how much vitamin D your skin can actually produce in that time.
If you’re unsure whether your current habits are giving you enough, paying attention to how you feel is a reasonable starting point. Fatigue, low mood, getting ill more than usual, and generally feeling run down are all associated with below-optimal vitamin D levels. None of those symptoms are specific to vitamin D alone, but if they’re familiar, and you haven’t checked your levels in a while, a blood test costs very little and gives you something concrete to act on rather than just guessing.
