The first thing I usually think of when someone says “vitamin D” is of course, the sun. That’s what you think of too, right? We know being in the sun is how we “get” vitamin D, so much so that it’s also known as the sunshine vitamin. But…
What is Vitamin D Needed for?
What is Vitamin D?
As daft as it seems, vitamin D isn’t actually a vitamin! It’s what’s known as a “pro hormone” or “precursor”, which basically means a substance that the body can then turn into a hormone (a hormone is just the term used to describe a substance in the body that can affect how our cells and bodily tissues function, by either up or down regulating certain bodily functions). In addition, the biologically active version (actually does something) of vitamin D is actually classed as a steroid hormone! But, before you go slamming vitamin D tablets before your next gym session, the “steroid” portion simply refers to the chemical structure of the hormone. Calm down there, Arnie.
What is Vitamin D needed for?
Vitamin D has quite a few functions, however its “main” function is:
Calcium and Phosphorus Homeostasis
Homeostasis is just that fancy word meaning “balance”. Our plasma levels of calcium are monitored and regulated fiercely – too little or too much plasma calcium can cause serious side effects [1,2]. If plasma calcium drops too low, the kidney produces biologically active forms of vitamin D called calcitriol. These little troopers are sent on their way to the intestines (where we absorb all the nutrients from food) and can significantly increase how much dietary calcium we absorb, from around 10-15% to around 30-40% which in turn leads to an increase in plasma calcium levels [3].
Phosphorus is another essential component of bone and tooth mineralisation (formation) and the absorption of it in the intestines can also be increased by our good old mate calcitriol [4]!
So when people associate calcium with strong bones and teeth, they should also put vitamin D in that bracket, too!
Vitamin D Deficiency
It’s ironic that on a planet that is quite literally powered by the sun – the ultimate provider of vitamin D – that almost 50% of the planet’s population are deficient in it [5]. Our lifestyles, which now involve being indoors for the majority of our lives, aren’t exactly ideal for the production of vitamin D. Environmental factors such as air pollution (which affects the ability of the sun’s UVB (Ultraviolet-B) rays to reach us – the ones we need to produce vitamin D) also play a part in deficiency. Other factors such as clothing and covering up too much, the time of day, the time of year and the colour of your skin are all other factors that affect how much vitamin D we’re able to produce from the sun.
Vitamin D deficiency can result in some very much unwanted side effects. Deficiency during childhood can lead to a condition known as rickets, where bones do not form properly and can become bowed and soft, and their growth stunted. In adults, a similar condition known as osteomalacia can occur in instances of severe vitamin D deficiency. This too results in softened bones and can ultimately lead to fractures due to poorer bone mineral density (related to bone strength).
How much Vitamin D do I need?
It depends on quite a few things really, like where you live and your diet. The higher up on the Earth you are (higher latitude), the more likely you are to need a vitamin D supplement. This is because those more northerly countries are exposed to less sunlight during winter – the days are shorter, we go out less and when we do our skin tends to be almost completely covered up because of the cold. Also, if your current diet doesn’t include many vitamin D-containing foods, then that’s obviously a pretty important factor in whether you could do with grabbing yourself a supplement.
In the UK, the Scientific Advisory Committee on Nutrition (SACN) recommend a reference nutrient intake (RNI) of 10µg (microgram) per day (also written as 400IU/day IU = international units) for those aged 4 and above. The RNI of 10µg/day is the amount of vitamin D supplementation that would be enough for 97.5% of the population to maintain the right level of serum vitamin D (amount in the blood) of > 25nmol/L [7].
What about under 4-year olds?
There isn’t currently enough evidence for RNI values to be set for children under 4, however instead, a ‘safe intake’ level has been advised. These are:
0-1 year old: 8.5-10µg/day (340-400IU/day)
1-4 year old: 10µg/day (400IU/day)
How do I get Vitamin D?
The sun, supplements and food.
The sun
In terms of how much time you need to spend in the sun to expose your skin to enough UVB rays to produce your daily requirement of vitamin D… this is very much an “it depends” answer again. It can depend on how much of your skin you’re showing e.g. are you wearing a long sleeve top and trousers, or t-shirt and shorts? Or are you lying down thus exposing more of yourself to the sun? It also quite significantly depends on the colour of your skin. Research has found fair-skinned people to only need around 20-30 minutes of sun exposure on their forearms and face during the middle of the day to allow the skin to synthesis the equivalent of 2000IU of vitamin D. It is also thought that only 2-3 exposures such as this per week are required to achieve and maintain normal vitamin D levels in the UK during summer [8].
However, those with darker skin may need to spend 2 to 10 times longer in the sun to achieve the same levels of vitamin D.
In addition, between October to April, many northerly countries just aren’t exposed to the sun’s UVB rays that we need to synthesis vitamin D, so in such times, we need to seek other sources, which leads us on to…
Food
While food can be a good source of vitamin D, the number of foods that contain a substantial amount of vitamin D are few and far between. Some good sources of vitamin D are: (per 100g)
Mackerel – 8.0µg
Salmon – 7.3µg
Sardines – 4.0µg
Egg – 3.2µg (one egg is ~50g-60g so ~1.6µg per egg)
Tuna (in brine, drained) – 1.1µg
Fortified breakfast cereals – Most breakfast cereals are fortified these days and are where a significant portion of the population get the majority of their daily vitamins.
So while you could get your daily vitamin D requirements from food, your selection of high vitamin D foods isn’t exactly broad and you would probably have to actively be trying to go for foods high in vitamin D. It’s unlikely you’re going to hit your daily requirement by accident.
Supplements
The easiest and most recommended option, especially in winter months. As previously mentioned, SACN recommend a daily supplement of at least 10µg (400IU) of vitamin D3. You can get vitamin D3 supplements in both capsule and oral spray form, the choice is up to you and your preferences. Some research has found both to be equally effective at improving vitamin D levels, however improved absorption from oral spray has been observed, too [9,10]. I personally use a spray.
So… Vitamin D, Get Yours!
Vitamin D deficiency is absolutely rife these days, do yourself a favour and don’t be a part of that statistic by making some tiny changes to your day. Whether that be including some high vitamin D foods or just gobbling a supplement capsule every morning, make sure you get yours!
Did you know?
Those with darker skin need to spend more time in the sun to produce the same amount of vitamin D compared to those with light skin. This is because darker skin contains more melanin, which absorbs more of the sun’s rays (ultraviolet-B rays) that would usually be used to synthesise vitamin D [6].
The ultraviolet-B rays we need to produce vitamin D are only reaching us when the sun is at a particular angle to us. How do we know when this is? Well… if your shadow is longer than you are, then you’re almost certainly not producing any vitamin D.
Take it easy!
Right I think that’ll do for vitamin D! I hope you’ve found this somewhat useful and it allows you to make an informed decision about how to proceed regarding your vitamin D intake.
Take it easy!
References
1. Fong J, Khan A. Hypocalcemia – Updates in primary diagnosis and management for primary care. Can Fam Physician. 2012;58(2): 158–162. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279267/
2. Turner JJO. Hypercalcaemia – presentation and management. Clinical Medicine (London). 2017; 17(3): 270–273. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6297576/
3. Nair R, Maseeh A. Vitamin D: The “sunshine” vitamin. Journal of Pharmacology & Pharmacotherapeutics. 2012; 3(2): 118–126. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3356951/
4. Fukumoto S. Phosphate metabolism and vitamin D. BoneKEy Reports.2014; 3: 497. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3944128/
5. Nair R, Maseeh A. Vitamin D: The “sunshine” vitamin. Journal of Pharmacology & Pharmacotherapeutics. 2012; 3(2): 118–126. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3356951/
6. Webb AR, Kazantzidis A, Kift RC, Farrar MD, Wilkinson J, Rhodes LE. Colour Counts: Sunlight and skin type as drivers of vitmain D deficiency at UK latitudes. Nutrients. 2018; 10(4): 457. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5946242/
7. Scientific Advisory Committee on Nutrition (SACN). Vitamin D and Health. [Internet]. 2016 [cited 2020 Dec 14]. Available from: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/537616/SACN_Vitamin_D_and_Health_report.pdf
8. Pearce SHS, Cheetham TD. Diagnosis and management of vitamin D deficiency. The British Medical Journal. 2010;340:b5664. Available from: https://doi.org/10.1136/bmj.b5664
9. Todd JJ, McSorley EM, Pourshahidi LK, Madigan SM, Laird E, Healy M, et al. Vitamin D3 supplementation in healthy adults: a comparison between capsule and oral spray solution as a method of delivery in a wintertime, randomised, open-label, cross-over study. British Journal of Nutrition. 2016 Oct;116(8):1402-1408. Available from: https://pubmed.ncbi.nlm.nih.gov/27724992/
