Vitamin D is often referred to as the sunshine vitamin because our bodies naturally produce it when the skin is exposed to sunlight. It plays a vital role in bone health, immune function, and muscle strength, as well as helping the body absorb calcium and phosphorus. Despite this, vitamin D deficiency is very common in the UK, especially during the darker months of the year. Understanding what causes vitamin D deficiency is important because low levels can affect energy, immunity, and overall wellbeing.

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Lack of Sunlight Exposure

One of the biggest causes of vitamin D deficiency is a lack of sunlight. In the UK, the sun is only strong enough for the skin to produce vitamin D between late March and early October. During autumn and winter, the angle of the sun prevents UVB rays from being powerful enough to trigger this process. Even during summer, many people spend long hours indoors at work or prefer to cover their skin with clothing or sun cream, which can reduce vitamin D production. While protecting the skin from damage is important, it also limits the body’s ability to make vitamin D naturally.

Dietary Limitations

Food sources of vitamin D are relatively limited. Oily fish such as salmon and mackerel, red meat, eggs, and fortified foods provide some vitamin D, but even with a healthy diet, it is difficult to meet daily needs without sunlight exposure. People who follow a vegetarian or vegan diet may be at higher risk of deficiency since most natural sources are animal-based. Although fortified foods like plant-based milks and cereals help, they often provide only small amounts, meaning diet alone is rarely enough to prevent low levels.

Skin Tone and Vitamin D Production

The amount of melanin in the skin affects how much vitamin D is produced from sunlight. People with darker skin tones naturally have more melanin, which provides protection from sun damage but also reduces the skin’s ability to make vitamin D. As a result, individuals with darker skin may need to rely more on dietary sources or supplements to maintain healthy levels, particularly when living in countries like the UK where sunlight is limited for much of the year.

Age and Vitamin D Absorption

As people get older, the body becomes less efficient at producing vitamin D from sunlight. The kidneys, which help convert vitamin D into its active form, also become less effective with age. Older adults may spend less time outdoors, further reducing sun exposure. This combination means vitamin D deficiency is especially common among older populations, increasing the risk of bone weakness and conditions such as osteoporosis.

Health Conditions and Medications

Certain medical conditions can interfere with vitamin D absorption or metabolism. Digestive disorders such as coeliac disease, Crohn’s disease, and ulcerative colitis may reduce the body’s ability to absorb vitamin D from food. Kidney and liver problems can also prevent vitamin D from being converted into its active form. Some medications, including those used for epilepsy and tuberculosis, can interfere with vitamin D metabolism, making deficiency more likely in long-term users.

Lifestyle and Cultural Factors

Lifestyle habits and cultural practices can also play a role. People who regularly cover most of their skin for cultural or religious reasons may not produce enough vitamin D, even during summer months. Those who work night shifts or spend most of their time indoors will also have limited exposure to sunlight, raising the risk of deficiency. Urban living can make things worse, as pollution can reduce the strength of UVB rays reaching the skin.

How to Prevent Vitamin D Deficiency

Public health guidance in the UK recommends that everyone considers taking a daily vitamin D supplement during autumn and winter, when sunlight is not strong enough. Those at higher risk, such as people with darker skin, individuals who spend little time outdoors, or those with dietary restrictions, may benefit from supplements all year round. Maintaining a balanced diet that includes sources of vitamin D can also help support levels, but supplements are often the most reliable way to ensure consistent intake.

Conclusion

Vitamin D deficiency can be caused by limited sun exposure, restricted diets, darker skin tones, ageing, certain health conditions, and lifestyle factors. Since it can be difficult to rely on sunlight and diet alone in the UK, supplements provide a practical solution for many people. Taking steps to maintain healthy levels of vitamin D is important for bone strength, immunity, and overall wellbeing.

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