Did you know that vitamin D is technically not a vitamin? A vitamin is usually something that we cannot make within our body, and that’s what makes vitamin D so special. It is the only vitamin that our body is able to make itself as if by magic* (*but it’s actually not magic it is simply the action of sunlight on our skin because vitamin D is in fact a hormone).
The majority of vitamin D (about 90%) is made in this way, but our ability to make vitamin D is influenced by so many external factors. If you think of anything that affects the ability of the sun to reach our skin, then that too will affect vitamin D production. Things such as, cloud cover, clothes and the pigment of our skin will affect how much vitamin D we can make. Wearing sunscreen is an important part of protecting our skin from sun damage; however it can reduce how much vitamin D we absorb. Recently a study has found when a broad spectrum SPF15 was applied at the recommended level, a sufficient level of vitamin D was produced while avoiding sunburn, which is great news considering that most of us get at least half our yearly dose of vitamin D while on summer holiday.
For those of us in the northern hemisphere, in particular anywhere north of Rome, we experience what’s called a vitamin D winter. This means that between October and March the sun is not in the correct angle for us to make vitamin D so for these months we are reliant on getting vitamin D from other sources, one of which can be our diet, however there are only a few sources where this is possible. Some of the food items that include vitamin D are; egg yolks, oily fish such as salmon, liver, fortified dairy products, fortified cereals, and even mushrooms that have been specially grown under UV light.
Vitamin D is involved in a complex dance with other nutrients such as calcium and phosphorus within our body, which helps us build and maintain healthy bones and muscles. This means that when we have enough calcium in our diet, while the vitamin D helps bind and absorb it so that we can get the most benefits out of it. However, when we do not get enough, it signals to our body to conserve calcium and when this is very low it means that we will use calcium from our bones. Over the long term, this can be damaging to our bones and means that those with a chronic deficiency are at risk of fractures or even developing conditions such as rickets in children and osteoporosis in adults. We have known about the importance of vitamin D in for our bones and muscles for some time but researchers are investigating other areas where our health may be affected by a lack of vitamin D.
Vitamin D sites are found in every cell in the body and it is
thought that a deficiency may limit some essential processes and affect our
health. For example, it has been linked to a rise in inflammation, with
increased risk of weight gain and diabetes, and over time can affect our heart
health. More recently, research has investigated the role that vitamin D plays
in fertility as it has been found that women who are vitamin D sufficient are
less likely to miscarry, with several studies showing that vitamin D may have a
potential beneficial effect on male and female fertility.
People who are at risk of deficiency include those who; avoid the sun, are pregnant, on a low fat or restrictive diet (such as vegan) , smokers, dark skinned and shift workers. These individuals, as well as vulnerable populations, such as children under 5 years and those over 65, should also take a supplement of 10ug/day, particularly from October to March. Additionally, babies who are breastfed are recommended to be given a supplement of 8.5ug/day as breast-milk contains low levels of vitamin D. (Formula is supplemented with Vitamin D so they do not need additional sources as long as they are getting +500mls/day).
About a third of the UK population is deficient in Vitamin D with increased rates in ethnic minority groups. While most people do not need to be tested for Vitamin D deficiency, those who experience bone pain, a recent fall or fracture and who are suspected of having osteomalacia, should follow up with their doctors. To conclude, everyone else and in particular at risk groups, should take a daily supplement as this will help support healthy maintenance of your vitamin D levels.
This post was written by Helena Scully, a Registered Nutritionist (ANutr) working as a Research Fellow on a Vitamin D project in St James's Hospital in Dublin. Since completing her undergraduate degree in Food Science and a Masters in Nutrition she has spent the last 7 years working in nutrition research focusing on maternal & childhood nutrition and bone health. You can find Helena on twitter @scully_helena
Andersen et al., (2015) ‘Vitamin D insufficiency is associated with increased risk of first-trimester miscarriage in the Odense Child Cohort’, AJCN, https://doi.org/10.3945/ajcn.114.103655
Crowe, et al., (2019) ‘Trends in the incidence of testing for vitamin D deficiency in primary care in the UK: a retrospective analysis of The Health Improvement Network (THIN), 2005–2015’.BMJ Open doi:10.1136/bmjopen-2018-028355
Gibney et al., (2005) ‘Introduction to Human Nutrition’ 2nd Edition, Nutrition Society, UK.
Pilz et al., (2018). The Role of Vitamin D in Fertility and during Pregnancy and Lactation: A Review of Clinical Data. Int J Environ Res Public Health. doi:10.3390/ijerph15102241
The British Dietetics Association (2016) ‘Food Fact Sheet—Vitamin D’ https://www.bda.uk.com/foodfacts/VitaminD.pdf Last Accessed: 30/10/2019
Young et al., (2019), ‘Optimal sunscreen use, during a sun holiday with a very high ultraviolet index, allows vitamin D synthesis without sunburn.’ Br J Dermatol. doi:10.1111/bjd.17888
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