Vitamin D

Vitamin D is a vitamin essential for bones, immunity, and many other functions.

What it is

Vitamin D is a fat-soluble vitamin, meaning it dissolves in fat and can be stored in your body's fatty tissues and liver. Unlike most other vitamins, your body can make its own vitamin D when your skin is exposed to sunlight. It's also found naturally in a few foods and is added to others.

There are two main forms of vitamin D:

• Vitamin D2 (ergocalciferol): This is found in plant-based foods and is also used in some fortified foods and supplements.
• Vitamin D3 (cholecalciferol): This is the form your body makes when exposed to sunlight, and it's also found in animal-based foods and some supplements.

Both forms are converted in your body to the active form of vitamin D, which is crucial for many bodily processes. In the UK, vitamin D levels are typically measured in nanomoles per litre (nmol/l). A normal range is generally considered to be between 50 and 375 nmol/l.

Why it matters

Vitamin D plays a vital role in keeping your body healthy. Its most well-known function is helping your body absorb calcium and phosphorus from your diet. These minerals are essential for building and maintaining strong bones and teeth. Without enough vitamin D, your body can't effectively use the calcium you consume, which can lead to weaker bones.

Beyond bone health, vitamin D is also thought to be important for:

• Immune system function: It helps to regulate your immune system, potentially playing a role in how your body fights off infections.
• Muscle function: It's involved in muscle strength and function.
• Cell growth: It plays a part in cell growth and development.
• Reducing inflammation: Some research suggests it may have anti-inflammatory properties.

What can cause it to be high or low

Low Vitamin D levels are quite common, especially in countries with less sunlight, like the UK. Several factors can contribute to this:

• Lack of sunlight exposure: This is the most significant factor. If you spend a lot of time indoors, wear clothing that covers most of your skin when outdoors, or live in an area with less sunshine, your body may not produce enough vitamin D.
• Dietary intake: Not eating enough vitamin D-rich foods can lead to lower levels.
• Skin pigmentation: Melanin, the pigment that gives skin its colour, reduces the skin's ability to absorb sunlight and produce vitamin D. People with darker skin may need more sun exposure than those with lighter skin to produce the same amount of vitamin D.
• Age: As people get older, their skin becomes less efficient at producing vitamin D.
• Certain medical conditions: Conditions affecting the gut, such as coeliac disease or Crohn's disease, can impair the absorption of vitamin D. Kidney and liver diseases can also affect how your body processes vitamin D.
• Obesity: Vitamin D can be trapped in fat tissue, making it less available to the body.
• Certain medications: Some medications can interfere with vitamin D metabolism.

High Vitamin D levels are much less common and are usually caused by taking very high doses of vitamin D supplements over a prolonged period. This can lead to a condition called vitamin D toxicity, where there's too much calcium in your blood (hypercalcaemia). Symptoms can include nausea, vomiting, weakness, frequent urination, and kidney problems. It's very difficult to get too much vitamin D from sunlight or diet alone.

Lifestyle factors that may help

Given that sunlight is a primary source of vitamin D, increasing sensible sun exposure can be beneficial. This typically means spending short periods outdoors during the sunnier months with some skin exposed, without getting sunburnt.

Dietary choices can also play a role. Including foods naturally rich in vitamin D or fortified with it can help maintain levels. Foods such as oily fish (like salmon, mackerel, and sardines), egg yolks, and fortified products like some margarines, cereals, and milk alternatives are sources.

For individuals who may struggle to get enough vitamin D through sunlight and diet, considering supplements might be an option, particularly during the darker months of the year.

Questions to discuss with your GP

If you're concerned about your vitamin D levels or have experienced symptoms that might be related to low vitamin D, it's a good idea to have a chat with your GP. Here are some questions you might consider discussing:

• What are the typical symptoms of low vitamin D, and could my symptoms be related?
• Would a blood test to check my vitamin D levels be appropriate for me?
• What is considered an optimal vitamin D level for my age and health status?
• Are there specific dietary changes or lifestyle adjustments you would recommend for me to help improve my vitamin D levels?
• Given my personal circumstances, would taking a vitamin D supplement be advisable, and if so, what dosage might be appropriate?
• Are there any underlying health conditions or medications I'm taking that might be affecting my vitamin D levels?