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The most important question any health professional can ask is ‘why? Digging deep to find and address underlying causes is the ultimate way to improve health; individually and globally.

There is a high prevalence of vitamin D deficiency worldwide.1 And as well as directly addressing the problem by raising awareness and promoting supplementation, it is important to ask ‘why’ this is happening?

In fact, there are many possible underlying reasons, and one major contributing factor is a lack of time spent outdoors in daylight. This is because, unlike most other essential nutrients, the main source of vitamin D is not food, but sunlight. Your skin actually makes vitamin D when it comes into contact with the sun’s UVB rays. If you’re not spending enough time outdoors however, this can’t happen. And this is where occupation can have a significant impact. Jobs that involve regular night shifts and / or high levels of time spent working indoors are associated with a higher risk of vitamin D deficiency.2-4

In a 2018 systematic review, researchers investigated whether occupations, specifically shift working and indoor working, are contributors to the increased incidence of vitamin D deficiency in industrialised nations.

Overall 90 papers were found; 10 of these that met the inclusion criteria were selected (9 cross-sectional studies and 1 systematic review).

Results showed that:

The majority of studies strongly indicate that the changing role of labour is at least contributing to the increased prevalence of vitamin D deficiency.

Indoor workers are commonly more susceptible to vitamin D deficiency than outdoor workers.

Outdoor workers are the least likely to suffer from low vitamin D.

• Health care professionals (especially those where training is involved), domestic workers and executives were found to have higher than average levels of deficiency, even in climates where there is possibility of high exposure to sunlight.

Shift workers and indoor workers are consistently reported as being the occupational group most likely to suffer from a deficiency of vitamin D.

The highest rate of vitamin D deficiency is found in those employed on night shift contracts no matter where the location.

The researchers commented,

“Certain occupations are suffering from, or have a predilection to suffer from, a deficiency of this vitamin. Shift workers and indoor workers are consistently reported as being the occupational group most likely to suffer from a deficiency of vitamin D3. It would appear prudent to investigate the potential of providing nutritional education to workers in addition to including preventative measures in the workplace.” 5

Vitamin D – What's the takeaway?

Whilst this research doesn’t necessarily tell us a lot that we didn’t already know about the high prevalence of vitamin D deficiency and the negative impact of not getting enough sunlight exposure. It does add an extra layer of detail to the picture, and encourages people to consciously evaluate the possible impact of their job on vitamin D levels.

The take away message is that if your job involves a lot of time spent indoors, it’s crucial to ensure you maximise daylight exposure when you can. And if you work night shifts, and have less opportunity to get outside in daylight, there’s even more reason to be vigilant about your vitamin D. We recommend you get your blood vitamin D levels tested regularly, find bare skin exposure to sunlight where you can and use vitamin D supplements when needed to keep your levels in the optimal range. Vitamin D is best supplemented as D3 (cholecalciferol) as this is the form naturally produced in the skin in response to sunlight. Vitamin D also works in synergy with vitamin K and these are often recommended together.

Do I need to take vitamin D supplements?

Guidelines from Public Health England recommend that everyone should take a daily vitamin D supplement throughout autumn and winter, and babies and children up to the age of 5 and anyone at higher risk should supplement all year round.6

If you are deficient however you will need to supplement with a course of vitamin D at higher levels. The easiest way to determine your vitamin D level is via a simple, finger-prick blood test which you can complete at home. These tests are relatively inexpensive and widely available online.

1. Cui A, Zhang T, et al. Global and regional prevalence of vitamin D deficiency in population-based studies from 2000 to 2022: a pooled analysis of 7.9 million participants. Front Nutr. 2023; 10: 1070808.
2. Rizza S, Pietroiusti A, et al. Monthly fluctuations in 25-hydroxy-vitamin D levels in day and rotating night shift hospital workers. J Endocrinol Invest. 2020 Nov; 43(11): 1655-1660.
3. Martelli M, Salvio G, et al. Shift work and serum vitamin D levels: a systematic review and meta-analysis. Int J Environ Res Public Health. 2022 Jul 22; 19(15): 8919.
4. Tang HY, Ko WS, et al. Relationship between serum 25 hydroxyvitamin D (25(OH)D) levels and mental health in shift female nurses. Sci Rep 2022; 12: 14583
5. Coppeta L, Papa F et al. Are shift work and indoor work related to D3 vitamin deficiency? A systematic review of current evidences. J Environ Public Health. 2018; 2018: 8468742
6. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/

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