The Vitamin D Gap for UK Workers
By Dr Suzanne Barr, HCPC-registered Dietitian and Founder of HercuWise. Last reviewed October 2026.
TLDR: from October to early March, the sun sits too low in UK skies for our skin to make enough vitamin D. The NHS advises everyone to consider a daily 10 microgram (400 IU) supplement over these months, and people who rarely get outdoors in the sunlight such as night-shift or indoor workers should take extra consideration.
The clocks go back next weekend in the UK (Sunday 25th October 2026). For a lot of people that means commuting in the dark, working under strip lights, and heading home in the dark again. If you work nights, you might barely see daylight at all, so it seems like a good moment to talk about vitamin D.
How we actually make it?
Most of our vitamin D doesn't come from food - it comes from sunlight. When UVB rays reach bare skin, they convert a cholesterol-related compound in the skin into vitamin D3. The liver and then the kidneys turn this into the active form the body uses.
Some of its key jobs are to help us manage calcium and phosphate, which we need for healthy bones, teeth and muscles (NHS).
But between October and early March the UVB just isn't strong enough in the UK. It doesn't matter how long you stand outside on a bright December lunchtime. Your skin won't make meaningful amounts. That applies across the whole UK, and in Scotland, Food Standards Scotland gives the same advice for October to March (FSS).
How common is low vitamin D?
More common than most people think. The latest UK National Diet and Nutrition Survey, (which includes data from 2019 to 2023), found 18% of adults aged 19 to 64 had deficient blood levels. In January to March, that rose to 31% (Office for Health Improvement and Disparities, 2025; MRC Epidemiology Unit).
Put simply, that's almost 1 in 3 working-age adults by late winter and the winter figure is about 1.7 times the year-round figure. "Deficient" in this context means a blood level below 25 nmol/L which is the threshold UK experts use for bone health risk (SACN, 2016).
What does deficiency do? In adults it can cause bone pain from a condition called osteomalacia, where bones soften (NHS). Muscle aches and weakness are also commonly reported. It tends to creep up slowly, so people often don't connect the dots.
Why shift and indoor workers deserve extra attention
This is the bit that doesn't get talked about enough in workplaces. The NHS lists people who are "not often outdoors" as a higher-risk group. Plenty of working adults fit that description without ever thinking of themselves as at risk. Think warehouse pickers, call centre staff, lab and factory workers, nurses on long days, office teams who eat lunch at their desks.
The research backs this up. A 2017 systematic review in BMC Public Health pooled 71 studies covering over 53,000 people. It found vitamin D deficiency in 80% of shift workers and 78% of indoor workers, compared with 48% of outdoor workers (Sowah et al., 2017). A second review in 2018 reached a similar conclusion: shift workers and indoor workers were consistently the groups most likely to be low (Coppeta et al., 2018).
Although these studies can't be directly comparable to UK workers, the direction of the evidence is interesting, especially as in the winter, everyone in the UK is in the same boat because the sun is too weak. The real additional disadvantage for night workers happens in summer. That's when the rest of us can top up our stores, and it's exactly when a night worker is asleep behind blackout blinds. So they can go into autumn already at higher risk of deficiency.
The TUC analysis of 2017 ONS Labour Force Survey data put the number of people in the UK who usually work nights at nearly 3.2 million, about 1 in 9 workers (TUC), so the numbers are significant. In Scotland it was 283,000 people in 2022, about 11% of workers (TUC analysis of LFS 2022). Care workers, nurses, drivers, security and warehouse staff make up a big share.
What the official advice says:
October to early March: everyone should consider a daily 10 microgram (400 IU) supplement (NHS).
All year round: consider it if you're rarely outdoors, live in a care home, usually cover most of your skin outside, or have darker skin (for example an African, African-Caribbean or South Asian background).
Don't overdo it: adults shouldn't take more than 100 micrograms (4,000 IU) a day unless a doctor tells you to. Too much over time can raise calcium levels and harm the kidneys and heart.
Labels can confuse: 1 microgram equals 40 IU, so 10 micrograms is 400 IU. Some labels still show an older EU reference of 5 micrograms; the UK recommendation is 10 (FSS).
Food helps, but it rarely covers it. Oily fish like salmon, mackerel and sardines, egg yolks, red meat and fortified spreads and cereals all contain some. UK cows' milk generally isn't fortified, so it's not a reliable source. That gap is the reason the supplement advice exists.
If you're experiencing any of the symptoms above it may be worth speaking to your GP to request blood tests, rather than guessing at doses. However NICE guidance actually advises against routine blood testing unless someone has symptoms or is at very high risk (NICE PH56). For most people, the supplement is the simpler route.
What employers can do:
A few easy nudges could include:
Share the NHS advice in early October, when the clocks change. That's when people are most receptive.
Make sure night teams, indoor-heavy roles and high risk employees get the message.
Night workers in Great Britain are entitled to a free health assessment under the Working Time Regulations. That's a natural point to signpost NHS guidance.
Encourage outdoor breaks from late March to September, especially for people on rotating shifts. Even short spells with forearms or legs uncovered help most people.
Signpost to guidance. Supplement choices belong with the individual and their GP or pharmacist.
This article is general information, not personal medical advice. If you're unsure, speak to your GP or pharmacist.
Want help building practical, evidence-based health support for your teams? Get in touch with HercuWise.
Sources
NHS. Vitamin D: vitamins and minerals. nhs.uk
Office for Health Improvement and Disparities (2025). National Diet and Nutrition Survey 2019 to 2023: report. gov.uk
MRC Epidemiology Unit, University of Cambridge (2025). NDNS 2019 to 2023: dietary deficiencies. epi.ims.cam.ac.uk
Scientific Advisory Committee on Nutrition (2016). Vitamin D and Health. gov.uk
NICE (2014). Vitamin D: supplement use in specific population groups (PH56). nice.org.uk
Food Standards Scotland. Vitamin D. foodstandards.gov.scot
Food Standards Scotland. Your questions on vitamin D answered. foodstandards.gov.scot
Sowah D, et al. (2017). Vitamin D levels and deficiency with different occupations: a systematic review. BMC Public Health 17:519. PMC5480134
Coppeta L, Papa F, Magrini A (2018). Are shiftwork and indoor work related to D3 vitamin deficiency? A systematic review of current evidences. Journal of Environmental and Public Health, 8468742. PMC6151365
TUC. Analysis of ONS Labour Force Survey on night workers (2017 data). tuc.org.uk
TUC. Night workers by occupation and UK nation (Labour Force Survey, April to June 2022). tuc.org.uk
NHS. Rickets and osteomalacia. nhs.uk
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