It's July, the sun is shining, and you naturally think: "at least I won't be short on vitamin D now." To a large extent you're right - summer really is the season when your body makes the most of it. But the data show something interesting: even in summer, some people still fall short. Let's look honestly at who they are and whether you need a supplement right now.
Sound familiar?
- You wonder whether you even need vitamin D in summer
- You work indoors all day and rarely get out in the sun
- You're older, or you keep yourself well covered from the sun
How the sun makes vitamin D
Vitamin D is unusual - you don't get it mainly from food; your body produces it in the skin under the action of UVB rays. That's why summer is the season when levels rise. A review notes that short sun exposures - on the order of 5-10 minutes on the arms and legs a few times a week - already contribute meaningfully (Holick, 2004).
But the same source lists the catch: the season, latitude, time of day, skin colour, age, sunscreen and even window glass all change how much is actually produced. In other words - the same sun does not give everyone the same result. And importantly: this is not an invitation to sunbathe. Excessive sun carries its own risks for the skin; we're talking about short, sensible exposures, without burning.
What the data show (honestly)
Here comes the most useful figure. A large analysis of data from nearly 56,000 Europeans found that the share of people with marked vitamin D deficiency was 17.7% during the winter months and 8.3% during the summer period (Cashman et al., 2016). So summer roughly halves the deficiency - confirming your intuition. But note: around 8% remain deficient even in summer. And if we raise the bar to higher levels, over 40% of people fall below it.
To be honest, none of these studies directly answers the question "do I need a supplement in July". But the conclusion is a reasonable one: for most people summer does a large part of the work, while for a real minority - it doesn't.
Who stays at risk even in summer
The literature reviews list the specific risk factors: little sun exposure, darker skin, excess weight, advanced age and absorption problems (Lips, 2006). Translated into practice:
- You work indoors and only go out in the morning and evening - the sun passes you by.
- You're older - the skin produces less vitamin D with the years.
- You keep well covered - covering clothing or constant sunscreen.
- Darker skin - more sun is needed for the same amount of vitamin D.
- Excess weight or absorption problems.
What the supplement actually does
The best-established role of vitamin D is for the bones - it helps the gut absorb calcium and so supports bone health. A large authoritative review notes that 400 IU a day prevents rickets and osteomalacia, and that with a real shortfall bone loss accelerates; the benefit for fractures is proven mainly in older people with a deficiency, at 800 IU together with adequate calcium (Bouillon et al., 2019). For effects beyond the bones, however, the same review describes the results as mixed.
And here's the important honest caveat. A large trial of nearly 26,000 people did not find that 2,000 IU of vitamin D a day reduced cancer or cardiovascular events (Manson et al., 2019). But its participants generally already had good levels. The right reading is: adding more when you already have enough doesn't buy you extra protection - not that vitamin D "doesn't work". It does its job where there's a real shortfall.
Caution: with vitamin D, more is definitely not better.
A telling trial in women over 70 found that a single huge annual dose of 500,000 IU not only didn't help - it increased falls and fractures compared with placebo (Sanders et al., 2010). That's evidence against "shock" mega-doses, not against sensible daily intake. Vitamin D is fat-soluble and accumulates - stick to the recommended dose and don't combine several sources at once.
π‘ Did you know...
- Vitamin D doesn't come mainly from food - your body produces it in the skin from the sun.
- In summer, the share of people in Europe with marked deficiency falls by about half - but not to zero.
- Sun through glass doesn't help - glass blocks the UVB rays that make vitamin D.
- With age, the skin produces less vitamin D, even with the same sun.
Summer does a large part of the work for you. The question isn't "does everyone need it", but "which camp are you in".
What to do in summer
- Get outside regularly - briefly, without burning, outside the strongest midday hours.
- If you're in a risk group, consider a supplement in summer too - don't rely on the season alone.
- If in doubt, get a blood test - it's the only accurate answer.
- Remember that autumn and winter are the seasons when the supplement matters most.
- Don't rely on mega-doses "all at once" - regular sensible intake is better.
Who are we to write about this
Cvetita Herbal has worked for over 10 years as a European manufacturer with its own European production and more than 1 million satisfied customers. It would be easy to tell you "everyone needs vitamin D" - but the truth is more precise and more useful. So we prefer to explain when it makes sense and when the sun is already doing the job. An informed choice is the better choice.
10/ten Vitamin D3
10/ten Vitamin D3 is a convenient tablet form with 400 IU per tablet - a sensible daily amount, not a shock dose. It makes the most sense if you're in a risk group during the summer, and especially in autumn and winter, when the sun no longer helps.
π‘ How to use it: Take it as directed on the packaging, ideally with a meal containing some fat - vitamin D is fat-soluble. If you have a diagnosed deficiency, your doctor may recommend a different amount - don't set high doses for yourself.
What to realistically expect
If you're at risk: the supplement covers the gap the sun doesn't fill - in summer too.
If your levels are good: extra intake doesn't bring bonus protection - don't expect more from it.
Keep in mind: autumn and winter are the real vitamin D season - plan ahead now.
What customers say
"I work in an office from morning till evening and practically never see the sun. My test results showed it in black and white - I take it all year round."
- Sarah T.
"At my age the doctor said my skin no longer produces enough. I take a sensible dose every day, without overdoing it."
- James H.
Frequently asked questions
Do I need vitamin D in summer?
For most people, summer does a large part of the work. But if you're in a risk group - little sun, older, covered or darker skin - a shortfall is possible even in summer.
How much sun is enough?
Short regular exposures of the arms and legs contribute meaningfully, but the amount depends on your skin, age and the time of day. Don't sunbathe and don't burn - excessive sun carries its own risks.
Is more vitamin D better?
No. It's fat-soluble and accumulates, and huge shock doses have proven harmful in trials. Stick to the recommended dose.
How do I know if I'm short?
With a blood test of your levels. It's the only accurate way, especially if you're in a risk group or have a medical condition.
Use the summer - get outside briefly and regularly. And if you're in a risk group or autumn is approaching, add a sensible daily dose instead of leaving it to chance.
GET VITAMIN D3Sources
- Holick MF. Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. Am J Clin Nutr, 2004. pubmed.ncbi.nlm.nih.gov/15585788
- Cashman KD et al. Vitamin D deficiency in Europe: pandemic? Am J Clin Nutr, 2016. pubmed.ncbi.nlm.nih.gov/26864360
- Lips P. Vitamin D physiology. Prog Biophys Mol Biol, 2006. pubmed.ncbi.nlm.nih.gov/16563471
- Bouillon R et al. Skeletal and extraskeletal actions of vitamin D: current evidence and outstanding questions. Endocr Rev, 2019. pubmed.ncbi.nlm.nih.gov/30321335
- Manson JE et al. Vitamin D supplements and prevention of cancer and cardiovascular disease (VITAL). N Engl J Med, 2019. pubmed.ncbi.nlm.nih.gov/30415629
- Sanders KM et al. Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial. JAMA, 2010. pubmed.ncbi.nlm.nih.gov/20460620
Food supplement. Does not replace a varied diet and a healthy lifestyle. It is not a medicine. Vitamin D is fat-soluble and accumulates - do not exceed the recommended dose. With kidney disease, sarcoidosis, medication, pregnancy or breastfeeding, consult a doctor. This information is for educational purposes and does not constitute medical advice.