Vitamin D: everything you need to know
We haven’t had a particularly sunny summer this year. However, even on the sunniest of days, we probably haven’t been able to maximise our production of vitamin D.
In this guide, I explore what vitamin D is, the foods that contain it, its critical roles in our body, the possible signs and symptoms of low vitamin D levels, and which populations are most at risk of deficiency. I also explain whether or not you should be supplementing vitamin D at this time of the year.
What is vitamin D?
Vitamin D, whilst technically a hormone, is often referred to as the “sunshine vitamin”. It plays a crucial role in maintaining our health and it's one of the essential nutrients that our body needs. Unlike most vitamins, our body can produce vitamin D naturally when exposed to sunlight.
However, in many parts of the world – especially those with long winters or high levels of pollution – getting enough sunlight year-round is a challenge. This is particularly the case in places like the UK, where short, grey winter days limit exposure to UVB rays, the type of sunlight responsible for stimulating vitamin D production.
And because vitamin D is mainly produced when our body is exposed to the summer sun, unfortunately between now and the end of April, the sun just isn’t strong enough – or high enough – to produce the amount of vitamin D we need to stay healthy and live better.
What does vitamin D do?
Vitamin D is essential for a wide range of functions within the body. Here are some of its primary roles:
Supporting bone health: vitamin D helps regulate the amount of calcium that gets absorbed into our bones, teeth and muscles, so it’s important in reducing the risk of osteopenia and osteoporosis.
Enhancing the immune system: vitamin D plays an important role in supporting the immune system. It helps the body fight off bacteria and viruses, which is why people with low levels may experience more frequent infections.
Improving muscle function: adequate levels of vitamin D are necessary for proper muscle function. Deficiency has been linked to muscle weakness and a higher risk of falls in older adults.
Improving mood: there is growing evidence suggesting that vitamin D may play a role in mood regulation and mental health. Low levels have been linked to conditions such as depression and Seasonal Affective Disorder (SAD), which tends to be more common in the winter months when sunlight is scarce.
Heart health: some studies suggest that vitamin D may have a protective effect on heart health by reducing the risk of hypertension and cardiovascular disease.
Supporting sleep: vitamin D is involved in the regulation of the body’s circadian rhythm. This rhythm is controlled by external factors, like sunlight, which also stimulates vitamin D production. Some studies have suggested that low levels of vitamin D may be linked to sleep disorders such as obstructive sleep apnoea, where breathing is interrupted during sleep.
Reducing inflammation: vitamin D helps to decrease the production of inflammatory proteins while promoting the production of anti-inflammatory ones. Inflammation is a key factor in autoimmune conditions such as rheumatoid arthritis, psoriasis and inflammatory bowel disease. Lower levels of the vitamin have been found in people living with an autoimmune condition.
Reducing Type 2 diabetes risk: studies suggest that vitamin D helps to improve insulin sensitivity and reduce insulin resistance, which is a factor in the development of Type 2 diabetes. Optimal vitamin D levels may also help the beta cells in the pancreas work more efficiently – leading to better glucose regulation.
Which foods contain vitamin D?
While sunlight is the most effective way to get vitamin D, dietary sources are also important – especially for individuals who have limited sun exposure or live in regions with long, dark winters. Some of the foods that are naturally high in vitamin D include:
Oily fish: fish like salmon, mackerel, tuna and sardines are excellent sources of vitamin D3. A 100-gram serving of salmon can provide up to 500-600 IU (International Units) of the vitamin.
Cod liver oil: a single tablespoon of cod liver oil can contain over 1,300 IU of vitamin D, making it one of the richest sources.
Egg yolks: eggs contain small amounts of vitamin D, with one large yolk providing around 40 IU.
Organ meats: organ meats, such as chicken and beef livers, also contain small amounts of vitamin D, with 100g of beef liver providing around 49 IU.
Mushrooms: some mushrooms, especially those exposed to UV light, can provide vitamin D2, though it is generally considered less effective at raising blood levels compared to D3.
What are the symptoms of low vitamin D?
Vitamin D deficiency is surprisingly common, and the symptoms can vary depending on the severity of the deficiency. Mild deficiencies may not cause any obvious symptoms, but more severe deficiencies can lead to:
Bone pain and frequent fractures: vitamin D deficiency can cause pain in the bones and lower back due to weakened bone structure.
Muscle weakness and cramps: weakness in the muscles can lead to difficulty performing everyday tasks or a higher risk of falls.
Unexplained fatigue: a lack of vitamin D can contribute to feeling tired or run down, even after a full night’s sleep.
Feeling low: low vitamin D levels have been linked to depression, anxiety and mood swings.
Frequent illness: since vitamin D is important for immune function, low levels can lead to more frequent colds, flu and other infections.
These symptoms are often overlooked as they don’t feel life-threatening.
Who’s at risk of vitamin D deficiency?
Unfortunately, we are all at risk of low vitamin D levels at this time of year but there are some groups of people who should be more cautious and aware of their levels:
Vegetarians and vegans: as some of the main food sources of vitamin D include oily fish, eggs and organ meat, those who chose to avoid these foods could be at risk.
Those with darker skin tones: the melanin in darker skin reduces the skin’s ability to produce vitamin D in response to sunlight.
Those over 65: as we age, our skin and kidneys become less efficient at synthesising vitamin D – and we often get less exposure to sunlight due to reduced mobility.
People who cover their skin: those who wear long clothing for cultural or religious reasons, or use sunscreen rigorously, may be at higher risk of deficiency.
Those living in northern latitudes: individuals living in places with long winters and limited sunlight, such as the UK, are at a higher risk. In fact, during the winter months, UVB rays are not strong enough to produce vitamin D in the skin.
People who are overweight or obese: vitamin D is fat-soluble, so it gets stored in fat tissue. This means that people with higher body fat may require more vitamin D to maintain adequate blood levels.
Those with certain health conditions: conditions such as inflammatory bowel disease, coeliac disease and cystic fibrosis make it difficult to absorb vitamin D.
Office and nightshift workers: if you work in an office, or during the night, you may be low in vitamin D as you naturally don’t spend as much time in the sunlight.
Those taking certain medications: medications such as antibiotics, anticonvulsants, antacids, corticosteroids, laxatives, calcium channel blockers and bile acid sequestrants can either deplete vitamin D or interfere with its absorption.
Those with a genetic variance: this makes producing, transporting and absorbing vitamin D a lot harder.
Should we be supplementing vitamin D?
Everyone should consider supplementing vitamin D at this time of the year as it plays such important roles in our body.
The NHS recommends everyone over the age of 4 supplementing with 10 micrograms (or 400 IU) every day between now and early April.
However, if you have kidney disease, high blood calcium or phosphorus levels, heart problems or sarcoidosis, then you should be careful about how much vitamin D you supplement as the vitamin can increase calcium levels and make your condition worse.
You also need to be mindful that if your vitamin D levels are already quite low, then this recommended amount is probably not going to provide any benefit. And if your levels are already adequate, and you supplement, you could end up with too much which can be toxic.
Your GP may be happy to test your levels but if not, I offer a simple, cost-effective finger-prick test you can do at home. The check includes:
An NHS-approved, finger-prick home test kit for you to complete and send to the lab. This just needs a few spots of blood dropping onto a card.
A short health history form for you to complete which I'll use to undertake a comprehensive safety check of your current medication, supplements and health history.
A personalised and appropriate vitamin D supplement dose based on your test result, weight and current supplementation levels (if supplementing).
A written recommendation for a supplement brand, form and any co-factor nutrients required to provide optimal vitamin D absorption for you.
10% discount on the recommended supplement(s).
All for just £60.
Are you ready to get your vitamin D levels checked?