As the days grow shorter and sunlight becomes a precious commodity in the UK, a silent health concern rises to the forefront: vitamin D deficiency. While many know it as the 'sunshine vitamin', experts emphasise that it is technically a hormone, manufactured by our bodies in response to sun exposure. This fundamental fact explains why so many Britons struggle to maintain adequate levels during the darker months from autumn through to spring.
What are the causes and risk factors?
Several interconnected factors can lead to a shortfall in vitamin D. The primary cause is a simple lack of sunlight. Nutritionist Maz Packham, founder of Nourishful Nutrition, clarifies that "we synthesise vitamin D in the skin in response to UVB light", making seasonal changes a major contributor. However, dermatologists strongly advise against unprotected sunbathing, noting that wearing SPF does not drastically interfere with vitamin D synthesis and is crucial for protecting against skin damage.
The risk is not uniform across the population. Individuals with darker skin tones, due to higher melanin levels, are more likely to have lower vitamin D levels as melanin reduces the skin's efficiency at producing the hormone. Furthermore, specific health conditions significantly increase vulnerability. Hannah Alderson, a registered BANT nutritionist, explains that vitamin D plays a role in reproduction and glucose balance, meaning people with PCOS have a staggering 67-85% prevalence of deficiency. Similarly, those with diabetes, Crohn's, coeliac disease, or poor gut health may struggle with absorption. For the elderly, a 2019 study placed the deficiency rate at around 37% for those aged 60 and over.
While diet can provide a small top-up—through foods like oily fish, eggs, and mushrooms—it is an unreliable main source. We typically get only about 10% of our required intake from food, making supplementation a necessary strategy for many.
Recognising the signs of deficiency
Vitamin D deficiency can manifest in a variety of ways, some more obvious than others. Nutritional therapist Eve Kalinik points to an unexplained susceptibility to infections and viruses as a primary signal, given the hormone's crucial role in immune function.
Other key signs to watch for include:
- Bone pain or muscle weakness
- Persistent low mood and fatigue
- Symptoms associated with Seasonal Affective Disorder (SAD)
According to different sources, SAD affects between 3% and 5% of the UK population. In severe cases, prolonged deficiency can lead to serious conditions like rickets in children or osteomalacia in adults, and in extreme circumstances, even seizures.
Practical steps to address a deficiency
The first and most crucial step is to determine your current levels. An at-home blood test can provide a good indication, but for a comprehensive analysis and personalised advice, consulting a GP or qualified healthcare provider is recommended.
When it comes to supplementation, the form and dosage matter. Supplements typically contain either vitamin D2 (ergocalciferol, from plant sources) or vitamin D3 (cholecalciferol, often from animal sources like lanolin). While it is difficult to reach toxic levels, vitamin D is fat-soluble, meaning it can build up in the body. Hannah Alderson cautions that "it's very hard to get vitamin D poisoning, but it is possible", underscoring the importance of correct dosing. Be mindful of 'mineral competition'—taking high doses of calcium, zinc, or magnesium simultaneously can hinder absorption.
Alongside supplementation, Maz Packham suggests trying to get 25 to 30 minutes of midday sun exposure when possible, as UVB levels are highest, making synthesis more efficient. Incorporating vitamin D-rich foods into your diet is also beneficial, though experts unanimously agree that for most people in the UK during winter, a high-quality supplement is the most reliable solution to maintain health and wellbeing.
