Can You Get Enough Vitamin D From the Sun in the UK, and When?

For most people, yes between late March and the end of September, and no between October and early March. The NHS says: "From about late March or early April to the end of September, most people should be able to make all the vitamin D they need from sunlight", and "between October and early March we do not make enough vitamin D from sunlight."¹ At UK latitude the UVB that skin needs does not reach the ground in winter, so the NHS says everyone "should consider taking a daily supplement containing 10 micrograms of vitamin D during the autumn and winter", and people whose skin gets or makes less from summer sun are advised to take one all year.¹ Part of the vitamin D guide and the vitamins and minerals guide.

When does UK sun make vitamin D?

Skin makes vitamin D when ultraviolet B (UVB) converts a precursor in the skin to previtamin D3, and UVB only gets through the atmosphere when the sun is high enough.² In the study that named the "vitamin D winter", skin exposed to cloudless sunlight at 52 degrees north, the latitude of the Midlands, produced no previtamin D3 from October through March.² NICE's clinical summary says UV levels are highest in the UK "between late March/early April and September", around midday, and "sunlight-induced vitamin D synthesis is only effective between these months in the UK".³ The National Diet and Nutrition Survey (NDNS Table 6.15, 2016 to 2023) shows the result: 6.1% of adults aged 19 to 64 were below 25 nmol/L of 25-hydroxyvitamin D in July to September, and 31.4% in January to March.⁴

How much summer sun does what?

Manchester studies reproduced summer sun in the laboratory. First, 120 white adults aged 20 to 60 received 1.3 standard erythemal doses three times a week for six weeks in a T-shirt and shorts: 90% reached 20 ng/mL (50 nmol/L) and 26.2% reached 32 ng/mL, equivalent to a summer of 13-minute midday exposures to 35% of the skin.⁵ In a year-long cohort of 125 white adults, levels peaked in September (mean 28.4 ng/mL) and bottomed in February (18.3 ng/mL), and "the majority of the population fails to reach this post-summer level and becomes vitamin D insufficient during the winter".⁶ The NHS, on its rickets and osteomalacia page: "try to get outside in the sun without wearing sunscreen for 15 minutes 2 or 3 times a week between late March and September – this may be more often if you have brown or black skin".⁷ The NHS vitamin D page adds: "always remember to cover up or protect your skin if you're out in the sun for long periods to reduce the risk of skin damage and skin cancer."¹

Does skin tone change what the sun makes?

Yes. Melanin absorbs part of the UVB; NICE says people with dark skin "may therefore need more sunlight exposure to produce the same amount of vitamin D".³ Given the same simulated summer as 109 white adults, 15 adults of South Asian origin saw a mean rise of 4.3 ng/mL against 10.5 ng/mL, and all stayed below 20 ng/mL while 90% of the white group reached it.⁸ In a dose-ranging study of 60 South Asian adults, exposures equivalent to 45 minutes or more of unshaded noon summer sun, three times a week, raised levels by a mean 8.7 ng/mL and brought 94% above 10 ng/mL (25 nmol/L).⁹ Over a year, 125 South Asian adults had a median of 9.0 ng/mL in summer and 5.8 in winter, against 26.2 and 18.9 in white adults: "The majority of South Asians never reached sufficiency in vitamin D status."¹⁰ The NHS advice follows pigmentation: "If you have dark skin – for example you have an African, African-Caribbean or south Asian background – you may also not make enough vitamin D from sunlight. You should consider taking a daily supplement containing 10 micrograms of vitamin D throughout the year."¹

Does age or body weight change it?

Skin from people aged 77 and 82 made less than half as much previtamin D3 under UV as skin from people aged 8 and 18: ageing "can decrease by greater than twofold the capacity of the skin to produce previtamin D3".¹¹ Weight works differently: after whole-body UV, the rise in blood vitamin D3 was 57% lower in obese adults (BMI 30 or more) than in lean adults, though their skin made it just as well;¹² in 686 adults, dilution in a larger body "fully explains their typically low vitamin D status".¹³

Does sunscreen block vitamin D?

In the laboratory, yes; in ordinary use, generally not. In a 1987 experiment, eight volunteers received one minimal erythema dose of UV: in the four without sunscreen, blood vitamin D3 rose from 1.5 to 25.6 ng/mL; in the four wearing SPF 8 it stayed at about 5 ng/mL.¹⁴ But NICE records SACN's view that most people "do not apply sunscreen at the recommended concentration, and do not apply it to all exposed areas of the skin", and that "normal usage of sunscreens does not generally prevent vitamin D synthesis".³

Can you get vitamin D through a window or from a lamp?

The NHS wording is "direct sunlight on the skin when outdoors", and the UK figures above come from exposure outdoors or under laboratory lamps reproducing summer sun, not daylight through glass.¹ The NHS does not list lamps among its sources of vitamin D: it names sunlight on the skin, a small number of foods and supplements.¹ The foods are on which foods are highest in vitamin D, and are mushrooms high in vitamin D covers the one food that makes vitamin D2 under UV.

Which time of day, and which part of the body?

Midday. UVB depends on the sun's height, so NICE says UV levels are highest "around midday", and the NHS says: "Spend time in the shade when the sun is at its strongest. In the UK, this is between 11am and 3pm from late March to September."^{3, 7} Early-morning and late-afternoon light carries little UVB. What the trials varied was the area of skin uncovered, 35% in a T-shirt and shorts: forearms, lower legs and face.^{5, 9}

Should I take vitamin D in summer too?

The NHS leaves summer open: "Between late March or early April to the end of September, most people can make all the vitamin D they need through sunlight on their skin and from a balanced diet. You may choose not to take a vitamin D supplement during these months."¹ Four groups are advised to take 10 micrograms all year: people who "are not often outdoors – for example, if they're frail or housebound", who "are in an institution like a care home", who "usually wear clothes that cover up most of their skin when outdoors", and people with dark skin.¹ The UK intake of 10 micrograms a day was set for the whole year; SACN "did not take account of sunlight exposure in making recommendations".¹⁵ Vitamin D contributes to the maintenance of normal bones, teeth and muscle function and to the normal function of the immune system, and from October to early March a 10 microgram supplement is how the NHS suggests most people cover the months the sun does not: "10 micrograms a day will be enough for most people", and "Do not take more than 100 micrograms (4,000 IU) of vitamin D a day as it could be harmful".¹ Timing is on the best time to take vitamin D; the NHS symptom list is on signs of vitamin D deficiency and the test route on how to check your vitamin D levels.

Frequently asked questions

How many minutes in the sun do you need for vitamin D?

In the Manchester trial, 13 minutes of midday summer sun three times a week on 35% of the skin took 90% of white adults to 50 nmol/L;⁵ the NHS says 15 minutes two or three times a week between late March and September, "more often if you have brown or black skin".⁷

How long does vitamin D from the sun last?

The storage form, 25-hydroxyvitamin D, "has a fairly long half-life of 2–3 weeks" (NICE);¹⁶ a UK tracer study measured about 15 days.¹⁷

Does the NHS recommend taking vitamin D in winter, and which months?

Yes: "everyone (including pregnant and breastfeeding women) should consider taking a daily supplement containing 10 micrograms of vitamin D during the autumn and winter", which the NHS defines as "between October and early March".¹

Can you get 10,000 IU of vitamin D from sunlight?

Sunlight is not measured in IU; the UK trials report blood levels.⁵ The NHS says "You cannot overdose on vitamin D through exposure to sunlight", and keeps the 100 microgram (4,000 IU) ceiling for supplements.¹

Sources

1. NHS. Vitamin D. Last reviewed 3 August 2020. nhs.uk.
2. Webb AR, et al. Influence of season and latitude on the cutaneous synthesis of vitamin D3. Journal of Clinical Endocrinology and Metabolism, 1988. PubMed 2839537.
3. NICE CKS. Vitamin D deficiency in adults: causes, August 2026. cks.nice.org.uk.
4. National Diet and Nutrition Survey 2019 to 2023, Table 6.15. gov.uk.
5. Rhodes LE, et al. Recommended summer sunlight exposure levels and 25(OH)D at UK latitudes. Journal of Investigative Dermatology, 2010. PubMed 20072137.
6. Webb AR, et al. Sunlight exposure and the vitamin D status of the UK white adult population. British Journal of Dermatology, 2010. PubMed 20716215.
7. NHS. Rickets and osteomalacia. Last reviewed 9 July 2025. nhs.uk.
8. Farrar MD, et al. Recommended summer sunlight exposure fails to produce sufficient vitamin D status in UK South Asian adults. American Journal of Clinical Nutrition, 2011. PubMed 21918215.
9. Farrar MD, et al. A dose range of simulated sunlight exposures in South Asian adults. American Journal of Clinical Nutrition, 2013. PubMed 23615828.
10. Kift R, et al. Lifestyle factors and lower vitamin D levels in UK South Asians. British Journal of Dermatology, 2013. PubMed 23855783.
11. MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. Journal of Clinical Investigation, 1985. PubMed 2997282.
12. Wortsman J, et al. Decreased bioavailability of vitamin D in obesity. American Journal of Clinical Nutrition, 2000. PubMed 10966885.
13. Drincic AT, et al. Volumetric dilution best explains the low vitamin D status of obesity. Obesity, 2012. PubMed 22262154.
14. Matsuoka LY, et al. Sunscreens suppress cutaneous vitamin D3 synthesis. Journal of Clinical Endocrinology and Metabolism, 1987. PubMed 3033008.
15. SACN. Vitamin D and health, 2016. gov.uk.
16. NICE CKS. Vitamin D deficiency in adults: diagnosis, August 2026. cks.nice.org.uk.
17. Jones KS, et al. 25(OH)D2 half-life is shorter than 25(OH)D3 half-life. Journal of Clinical Endocrinology and Metabolism, 2014. PubMed 24885631.