Last year, the SACN Vitamin D health report was released in the UK, and it’s now recommended that everyone in the UK takes a vitamin D supplement over the winter months (October to March ish, because our weather is just that crap). This is especially important for certain groups of people who are more vulnerable.
What actually is vitamin D though?
Vitamin D is actually a group of fat-soluble compounds, the most important ones of which are D2 and D3. These vitamins are responsible for increasing intestinal absorption of things like calcium, iron, magnesium, phosphate, and zinc. All of these are super important for healthy bones, teeth, and muscles.
As you might therefore expect, vitamin D deficiency can cause bones to become soft and weak. In children it can lead to rickets, whereas in adults it can lead to osteomalacia. You can’t overdose on vitamin D from sunlight due to the feedback mechanisms in your body, but you can from supplementation. The main issues around this relate to hypercalcaemia (too high calcium), so nausea, vomiting, lack of appetite, nervousness, weakness, and ultimately renal failure. Not good, and just goes to show too much of a good thing really is a bad thing!
Vitamin D deficiency has been linked to bone issues, as well as increased risk of viral infections like flu, as vitamin D helps to activate the innate immune system and dampen the adaptive immune system. However, this is just a relationship, and as I keep shouting from the rooftops: correlation does not equal causation! In fact, vitamin D supplementation doesn’t seem to have many effects. It has no meaningful effect on risk of stroke, cardiovascular disease, blood pressure, diabetes, cancer, autoimmune disorders, infections, or risk of bone fractures. There may be a slight decrease in mortality with supplementation in the elderly, but in the end low vitamin D levels may actually result from disease rather than causing it. Supplementation only really seems to be useful if you’re already deficient.
How do you get it?
There are three main ways to get your vitamin D on: (1) sunlight, (2) food, and (3) supplements.
Exposing your bare skin to sunlight is the simplest way to get vitamin D. You don’t need to spend hours outside getting tanned or sunburnt – in fact please don’t get burnt! – just around half the time it takes for your skin to start turning pink. The more skin you expose the more vitamin D is produced, but exactly how much also depends on where you live, the colour of your skin, and what time of day it is.
If you’re sitting inside by a window, even if the sun is shining directly on you, your body won’t be able to make vitamin D, as ultraviolet B (UVB) rays can’t actually get through the glass. If you are outside and the UVB rays hit your skin, a biologically inactive form of vitamin D is produced in your skin, after which enzymes in your liver and kidneys activate it.
In the UK in winter, there just aren’t enough hours of sunlight, and the sunlight you do get doesn’t contain enough UVB for you to get your vitamin D needs – not ideal! Which brings us to the next source…
There aren’t a great many foods that are good sources of vitamin D, mainly oily fish like salmon, mackerel, herring etc., red meat, and egg yolks. Some mushrooms also contain vitamin D, and you’ll often find non-dairy milks and breakfast cereals are fortified with vitamin D. Don’t worry about losing the vitamin D when you cook these foods, as around 70-90% of the vitamin is retained after boiling, frying, and baking.However, despite all that, unless you’re eating a ridiculous amount of these foods, you’re not really going to get all the vitamin D you need. So that just leaves the third option…
As I mentioned, in winter it’s recommended that everyone in the UK takes a vitamin D supplement. Everyone. But certain groups of individuals are recommended to take one throughout the year: for example babies and children up to age 4, and people who are not often exposed to the sun. This latter group can include people who are housebound, people in care homes, and people who usually wear clothes that cover up most of their skin outdoors. These at-risk individuals are recommended to take a daily supplement of 10 micrograms (10µg or 400 IU) per day.
Ultimately, you only really need to supplement if you’re living somewhere horrible and grey in winter, if you’re at risk due to considerable lack of sunlight, or if you’re already deficient. If you’re not sure, then taking a daily supplement isn’t likely to do any harm, as long as you stick to the guidelines of 10µg per day. Going considerably over this is probably not going to end well. If you’re already taking a multivitamin it’s also worth checking if it already includes vitamin D as then you don’t need to worry!
Now who’s excited for summer?!
NHS advice on vitamin D
The effect of vitamin D supplementation on skeletal, vascular, or cancer outcomes: a trial sequential meta-analysis
Effect of Vitamin D Supplementation on Blood Pressure
Vitamin D and innate and adaptive immunity
Vitamin D and calcium: a systematic review of health outcomes
SACN Vitamin D and health report