Vitamin D
The pandemic raised awareness of the importance of vitamin D. In this post I outline it’s main body functions, and answer: where do you get it from, how much do you need, can you have too much and who is at greater risk of deficiency.
Why is vitamin D important?
The main function of Vitamin D is to control the level of calcium in your body, especially your bones, and maintain optimal bone density. This is important at any age, but especially to help prevent osteopenia/osteoporosis with ageing.
Vitamin D is crucial for the immune system: it boosts your innate immunity to help fight against infection and it also inhibits the development of autoimmunity, particularly multiple sclerosis and inflammatory bowel disease. Vitamin D also reduces inflammation and improves your gut health.
Low vitamin D levels have been associated with Seasonal Affective Disorder (SAD) and low mood.
Where do we get Vitamin D from?
Vitamins are not made in the body – we get them from food. Vitamin D isn’t actually a vitamin – it’s a hormone and it is made in the skin from exposing a form of cholesterol to UV sunlight. Our bodies can also store it, so we can draw on these reserves when sunlight is not available. When these reserves are insufficient, such as during the winter months, exogenous sources are required. While there may be sunlight during the winter, this contains insufficient UV radiation for vitamin D synthesis.
There are few dietary sources of vitamin D – oily fish are the richest source: salmon, mackerel, anchovies, sardines, herring (SMASH). Other sources include liver, eggs, butter, fortified milk and mushrooms. But we can’t get enough Vitamin D from these.
How much vitamin D do we need?
The debate continues as to what is the optimal level of Vitamin D and there is a lack of consensus. It is always best to start with a blood test so you know your current level. Most GPs will include this as part of a standard full blood count or you can get a quick finger prick test done. You definitely want your level to be above 50 nmol/L and above 75 nmol/L is optimal.
Can you have too much Vitamin D?
You will never make too much vitamin D from sunlight exposure because your body inherently regulates this. Many doctors and practitioners recommend taking very high supplemental levels. While they have to be extremely high to achieve toxicity, excessively high doses are unlikely to achieve corresponding additional health benefits. You should not take more than 4000iu a day. The basic supplement dose for adults is 1000iu and this is quite safe.
Who is at greater risk of Vitamin D deficiency?
Certain groups of people are at higher risk of deficiency and are likely to need supplementation either all year round and/or at higher doses.
As we age, the ability of our skin to synthesise vitamin D declines - institutionalized elderly patients are almost all deficient.
Those living in temperate climates such as the UK may not get enough sun exposure especially if they do not spend enough time outdoors.
Fairer skins synthesise vitamin D more effectively than darker skins. Those who keep their skin covered with clothing will not be producing enough vitamin D as the skin needs direct sun exposure.
Individuals with a history of liver or kidney disease, or with poor fat absorption (because Vitamin D is absorbed with the help of fat), may also be at risk of deficiency.