There are high levels of vitamin D deficiency in the UK population, because the sun’s UBV rays are not strong enough in the autumn and winter months to allow the synthesis of vitamin D in the skin. People living in cities who typically spend less time outside are at increased risk of deficiency.
Why do we need vitamin D?
We know that vitamin D supports healthy bones and teeth and this essential fat-soluble nutrient has been linked to a wide variety of other health benefits, such as supporting bone health and the prevention of osteoporosis. Without sufficient vitamin D, alongside vitamin K2, for example, we may struggle to absorb enough calcium into our bones, which could weaken them.1
Research has also shown that vitamin D deficiency is linked to a higher risk of obesity, cardiovascular problems, autoimmune conditions, depression, and even several types of cancer.2,3 It’s clear that maintaining optimal vitamin D levels has considerable wellness potential.
Where do we get vitamin D from?
We should aim to get everything we need from our diet, however, in the case of vitamin D, we can only get a small amount from our diet. This is mainly from animal-based foods such as oily fish, liver, egg yolks, some fortified cereals, drinks, and dairy.
The bottom line is, we can’t reasonably rely on diet alone to provide us with enough vitamin D. To put this into perspective, you would need to eat 22 eggs to get the same level of Vitamin D in a single supplement.
Vegetarians and vegans struggle to get vitamin D from their diets; research suggests the vegetarian form of vitamin D (vitamin D2) is not absorbed as effectively by our bodies as the animal form, D3.4
The main source of vitamin D comes from sunshine on our bare skin. When skin is exposed to the sun, UVB rays combine with cholesterol to synthesise a type of vitamin D. This is then transported to the liver and kidneys where it’s then activated. Unfortunately, there are many factors that can affect how we make vitamin D from sun exposure. What’s more, for everyone in the UK, it is not possible to synthesis vitamin D from sunlight during autumn and winter as the sun’s UVB rays aren’t strong enough during the colder months.
What factors can affect how we absorb vitamin D from the sun?
Even during sunnier months, clouds may restrict the amount of vitamin D we can make by preventing UVB rays from reaching our skin in enough quantity. This problem is compounded when living in a large city: tall buildings can act like clouds, preventing the sun’s rays from reaching our skin.
Pollution can also be a problem for city dwellers, with smog and air pollution further hindering UVB rays from reaching us. In fact, researchers have found that due to the low ground level of UV light, there is a direct correlation between the level of air pollution and the risk of vitamin D deficiency.5,6
Work and lifestyle
Another factor effecting city workers is simply the lack of time spent outside: many people who work in cities tend to spend most of their working day in an office. The sun emits various types of UV rays, but it’s the UVB type which is needed to produce vitamin D in the skin. This type of sun ray is stopped by most types of glass. So, even if your desk is next to a window, you still wouldn’t get enough UVB to make sufficient vitamin D – and that’s if you’re lucky enough to sit by a window.
Long working hours and lengthy commutes reduce time spent outside whereby UBV rays reach the skin. In fact, some studies show that Brits get out of the house less than two hours a day on average.7 Think about it: if you live in a city, how long do you think you spend outside during the day?
How to supplement your vitamin D levels
Given the rising numbers of people with vitamin D deficiencies, the UK Department of Health now advises that we all take a vitamin D supplement from October to April. However, given the increased risk for urban dwellers to experience potential year-round deficiency, if you do live in the city, then it might be worth thinking about taking a vitamin D supplement for the full 12 months of the year.
Ultimately, the amount of vitamin D we need varies hugely between individuals. However, research suggest that a daily supplement dose of 1000 to 2000IU of vitamin D3 (25 to 50mcg) is about the right amount to support most people’s ability to achieve a vitamin D level of at least 75nmol/L required for optimal health.8
1.Cranney A, Horsley T, O'Donnell S, Weiler H, Puil L, Ooi D, Atkinson S, Ward L, Moher D, Hanley D, Fang M, Yazdi F, Garritty C, Sampson M, Barrowman N, Tsertsvadze A, Mamaladze V (2007), Effectiveness and safety of vitamin D in relation to bone health, Evid Rep Technol Assess (Full Rep) (158):1-235.
2.Bischoff-Ferrari HA (2014) Optimal serum 25-hydroxyvitamin D levels for multiple health outcomes, Adv Exp Med Biol., 810:500-25.
3.Giovannucci E, Liu Y, Hollis B, Rimm E, (2008) 25-Hydroxyvitamin D and Risk of Myocardial Infarction in MenA Prospective Study, Arch Intern Med., 168(11):1174-1180.
4.L. Tripkovic, H. Lambert, K. Hart, C. P. Smith, G. Bucca, S. Penson, G. Chope, E. Hypponen, J. Berry, R. Vieth, S. Lanham-New (2012) Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition 95 (6): 1357.
5.Feizabad E, Hossein-Nezhad A, Maghbooli Z, Ramezani M, Hashemian R, Moattari S (2017) Impact of air pollution on vitamin D deficiency and bone health in adolescents, Arch Osteoporos. 12(1):34.
6.Hosseinpanah F, Pour SH, Heibatollahi M, Moghbel N, Asefzade S, Azizi F (2010) The effects of air pollution on vitamin D status in healthy women: a cross sectional study, BMC Public Health, 29;10:519.
8.Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad H, Weaver CM (2011) Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 96:1911-30.