Vitamin D has rapidly become centre attention in the world of nutrition, and many more doctors are testing for it these days. But what is it? Why do we need it? How do we get it? And should we be supplementing with it? We’ll unravel the dark mysteries of this vitamin that’s not actually a vitamin at all.
What is vitamin D?
Unlike true vitamins, vitamin D is a hormone called calcitriol. Also, unlike other vitamins, we don’t really get much of it from our diet – it mostly comes from direct sunlight, giving it the nickname the sunshine vitamin.
It’s important to note that the type of sunrays that we need to make vitamin D in our bodies cannot penetrate glass, and so you need to be outside to benefit.
Vitamin D is important for the absorption of calcium and phosphorus, minerals that are essential for good teeth and bones.
During the winter, the sun rays produce inadequate wavelength to make vitamin D so we need to ensure we get enough during the summer to see us through, therefore we need to rely on a good diet. Some people may need to supplement, particularly the elderly, and very young children.
The sun provides us with around 90% of our Vitamin D needs, and is very limited in foods. It is available in oily fish and eggs, so if you are a strict vegetarian or vegan, you may consider vitamin D supplementation, although many food products are now fortified with it!
If you enjoy eating mushrooms, these do make vitamin D, so leaving them in direct sunlight (not through glass!) for an hour will naturally fortify them.
Vitamin D is also found in cocoa surprisingly! Recent research has found that cocoa beans that have been fermented and then dried out in the sun actually make vitamin D – although the highest amounts are found in dark chocolate.
You can also get a test from your GP if you think you may have a deficiency (although due to costs, many GPs may not offer it), and if you have very dark skin, or skin that is covered up a lot, you could be vulnerable to inadequate amounts.
What does vitamin D do?
The more scientists study vitamin D, the more they’re understanding its function within the body. The current thinking is that vitamin D, apart from helping the absorption of calcium and phosphorus into the blood, also:
- supports the immune function, thus giving you a robust defence system against infection
- supports muscle function, and therefore may help elderly preserve muscle function in conjunction with strength exercises (1)
- necessary for a healthy heart and circulation
- keeps the lungs functioning properly
- important for brain development
- and more recently, possibly has a protective role against cancer
Inadequate vitamin D
It is estimated that around 20% of us have low vitamin D status and that rises in the winter to up to 40% (2).
It has also been suggested that low vitamin D may be linked to conditions such as diabetes (3), multiple sclerosis (4) and adequate levels could also potentially protect against some autoimmune diseases (5).
Low levels of vitamin D have been linked with depression in females. According to the Oregon State University, a study on young healthy women showed that those who suffered significant depressive symptoms had vitamin D levels that were too low for good health (6).
Optimising vitamin D
Fat and vitamin D
Vitamin D is a fat-soluble vitamin, this means that it needs to “ride” on a fat particle in order to be absorbed into the body, so if you supplement, then you will need to take it with something that has fat in it, so that it can attach itself during the digestion and absorption process and get into the blood.
Magnesium and vitamin D
Studies suggest that people with low vitamin D may have insufficient magnesium in order to allow the body to make vitamin D from the sun (7).
Conversely, people who have sufficient magnesium are less likely to have deficiency in vitamin D.
Magnesium is a cofactor in the production of vitamin D, whether we get vitamin D from the sun or from our food. If we don’t get enough magnesium, vitamin D production stops.
Supplementing with magnesium does appear to improve our ability to make vitamin D according to one study (8).
Magnesium is easily supplemented by using skin sprays or taking baths with Epsom salts, as magnesium can absorb through the skin (9).
Vitamin D and Sun Protection Lotions
There’s been some debate over whether applying sun protection creams or lotions can block the effect of producing vitamin D, particularly at high SPF factors.
Several studies over the years have remained relatively inconclusive on this issue; mainly because no one applies these creams in an even, controlled fashion and we’re notoriously bad at re-applying creams after activities such as swimming or playing beach games etc.
The bottom line is, sun protection is important to prevent malignant skin lesions. However, leaving the skin unprotected for 10-15 minutes for light skinned people and 15-20 minutes for darker skinned each day should be adequate to ensure vitamin D is “topped up” (vitamin D is stored in the liver), and then apply the sunscreen.
To be honest, if you’re out in the sun long enough, no amount of sun cream is likely to cause you vitamin D deficiency – we’re just not that good at applying it! So never use the vitamin D excuse for not protecting your skin from sun radiation.
Vitamin D Supplementation
There is (currently) no daily recommended amount of vitamin D specified for optimal health. The UK Government suggests that an active (outdoors) lifestyle with adequate dietary intake of vitamin D should be sufficient for most healthy adults.
Vulnerable people such as those who are housebound, institutionalised (long term hospital care, prisons etc), or who cover most of their skin for personal or cultural reasons, may need to supplement because they are at most risk of deficiency.
Vegans often have to supplement too, but bare in mind that most supplements are not vegan-friendly.
However, no supplement should be taken if other medications are being taken without full knowledge of your medical advisor.
The SACN 2016 report on vitamin D and health (2) suggested that adults probably should aim for around 10μg (400IU) daily, and children under 4 years 8.5-10μg (340-400 IU) to prevent vitamin D dropping below deficient status (see table below).
The safe upper limit of supplementing vitamin D is currently set at 100μg (4000 IU) daily for adults and half this for children under 10.
What this means is, dosages higher than this may cause excess calcium in the blood, which could cause kidney stones.
In rare cases, a condition called hypervitaminosis D could occur, which is where you have too much vitamin D, causing high blood pressure and poor kidney function.
Most of us should be able to get adequate vitamin D simply by going outdoors everyday, exposing our legs or arms to the sun for around 15 minutes.
However, if you do supplement, the type that is most likely to get into your body system and do what it is supposed to do is vitamin D3 (not D2 as many supplements supply).
For dosing, unless you know you are deficient, Public Health England recommends that we need 10mcg (400 IU) of vitamin D daily for healthy bones, teeth and muscles.
A word about combining supplements
Many of us are unaware of what each type of supplement contains, and because it is now common to want to take single supplements, I should give you a few warnings.
First, be very cautious about taking a vitamin D supplement if you’re also taking a fish oil supplement or cod liver oil. Both of these contain vitamin A and vitamin D. You could go over your daily recommended dosage.
Never take single vitamin supplements along side multi-vitamins unless you’re under medical supervision, because you are at risk of vitamin poisoning.
The bottom line is, don’t go into your local pharmacy or supermarket and come out with a sack full of supplements unless you really know what you’re buying and you have had advice from a registered dietitian, nutritionist, nutritional therapist or GP.
Never take supplements if you are on medication without speaking to a pharmacist or GP first.
Vitamin D Testing
GPs can arrange a vitamin D test, but don’t expect many to be that receptive to it. Remember, it will be a cost that they may see as unnecessary.
True vitamin D deficiency is rare, and when it happens, it causes Rickets. Rickets in children is worryingly starting to increase, so kids could be vulnerable and thus children under the age of 5 are often advised to take supplements.
Below is a table that will guide you should you have the test and decide whether to supplement or not.
|Vitamin D dosage (if tested deficient or low status)|
|<25nmol/L||Deficient||You should be under medical supervision||~2000 IU daily|
|25-50nmol/L||Low status||Stores of vitamin D are low so you should really supplement||~1000 IU daily|
|51-75nmol/L||Adequate||There is no strong argument for supplementation- get more sun and eat well||800 IU daily|
|>75nmol/L||Optimal||Perfect, keep up the good work!||Nil|
10mcg (400IU) of vitamin D will increase blood levels by 10nmol/L (8)
Seb is a writer and blogger of food and nutrition. He holds a bachelors and a masters degree in nutrition science, and has studied sports and exercise nutrition at postgraduate level. He specialises in plant-based nutrition and believes passionately that we can all live with a little less meat. He writes for www.veggieandspice.com and www.itsaboutnutrition.com