Vitamin D supplementation is essential
For the ones who don't have much time, here is the take-home message:
From October to April, we all - children and adults alike - need to take a supplement of vitamin D to ensure optimal bone health and strengthen our immune functions.
A minimum of 10µg (or 400IU) of vitamin D3 is recommended.
And for the ones who want to know why, here is full story:
Vitamin D is a funny one - it isn't truly a vitamin in the original sense of the word. It is an essential nutrient for our metabolism but, unlike other vitamins, its dietary component is marginal. Our main source is from the sun: we synthesise it when we expose our skin to the UVBs.
Why we need Vitamin D
Vitamin D is well known for its critical role in muscle, teeth and bone health, enabling the calcium to be fixed onto our bones. A chronic deficiency in this nutrient would result in rickets in children and osteoporosis in adults. But that's not it.
More recent studies have shown that vitamin D plays also a role on many other aspects of your health. There is more and more evidence that good level of vitamin D is a protective factor against heart disease, diabetes, cancer and tuberculosis (Holick, 2004). It is believed it could also act on asthma (Martineau et al., 2016) and possibly on mental health (Gowda et al, 2015).
And even more recently, it has been shown that it could help with our immune functions and protect us against the common cold (Martineau et al., 2017).
A lot of very good reason to keep our level up!
How to ensure we have a good level of vitamin D
Optimal blood level of vitamin D is defined by a serum level of 25(OH)D3 above 50nmol/l. To maintain such a level, a recent study has shown we need to get more than 30µg of vitamin D per day (Smith & Hart, 2017).
To reach this, we can eat lots of oily fish, egg yolks, vitamin D fortified food (cereals and milk) and even mushrooms. But average dietary intake in adults in the UK is only around 3 µg/day (SACN, 2016). The rest will need to come from the sun. This is easily done during the summer months: a 15mins skin exposure, at 11 am in July, to the sun's UVBs should provide all the vitamin D we need. But in winter this is not the case, even during a sunny day, because the sun is too low for us to get the UVB rays we need.
From October to April, in Europe, the only option is to get our daily dose of vitamin D through supplementation.
How much vitamin D supplement should we take
Unfortunately, there isn't a clear answer. It will depend on one’s current vitamin D blood level which can vary from one person to another depending on diet, skin complexion (dark skinned people tend to be more depleted in the UK), lifestyle (e.g. use of suncream, time spent outdoors) and cultural habits (e.g. clothing and skin exposure).
But one thing is sure is that a big portion of the population could do with more. The latest UK National Diet and Nutrition Survey (NDNS, Sept 2016) showed that low vitamin D statuses were present in all age groups.
As result, Public Health England published new recommendations in July 2016:
Breast-fed babies should take 8.5 - 10 µg/day of vitamin D supplement all year round;
Formula-fed do not need to take supplementation since formulas are already fortified in vitamin D;
Children and adults should take 10µg/day of vitamin D supplement from October to April;
Population at risk of deficiency should take 10 µg/day of vitamin D supplement all year round.
For fully detailed recommendations, check NHS choice
But some scientists argue that these recommendations are on the conservative side (Science Media Centre, 2016). For example, the US recommendation is to take 15 µg/day (600 IU) and even that is considered to be low.
The truth is that this UK recommendation is based on two things: first of all, it only takes in account the existing evidence gathered for many years around bone health and vitamin D and does not consider the other beneficial aspects of vitamin D because we don’t have enough solid data on them yet; and secondly, since the original recommendation was nil, the new target had to be manageable. To put in other words, if we manage to get everyone in the UK to take a supplement of 10 µg/day is will already be a major progress for people’s bone health… yet, maybe we could do with a higher dose.
But how much then?
That we do not know. And the UK does not suggest an upper limit. Yet, excessive vitamin D can be toxic. If hypervitaminosis D does not occur from excessive exposure to sunshine (although dermatologists do not recommend it!) or dietary intake, it can happen from too much vitamin D supplements. Serious signs of toxicity (nausea, kidney stones, muscle weakness) have been observed in patients who took high dose of vitamin D on a daily basis and, for that reason, the US recommend not to take more than 100 µg/day (4,000 IU).
So, if you take several food supplements (e.g., multivitamin + calcium + vitamin D), do check the labels and add it all up to make sure you don’t take more than 100 µg/day (4,000 IU) a day of vitamin D.
Which type of vitamin D to choose
You might notice two types of vitamin D on offer: vitamin D2 and D3. One is from plant source (D2), the other is mainly from animal-source (D3). But there are not equal. The D3 is 50% better at raising our vitamin D blood level (Tripkovic et al, 2012). So, unless you are vegan, my advice is to choose Vitamin D3. And if you are vegan, do check the labels as some vitamin D3 supplements are vegan-friendly.
As for the form - tablets, capsules, drops or spray – they all work so choose the one that suits you and your family best (Todd et al, 2016).
In all cases, stock up and take your daily dose.