By Shelley Osborne-Shaw
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September 1, 2025
Vitamin D 10 years ago, I discovered just how important vitamin D could be to our health when I was diagnosed with a deficiency. At the time, I was struggling with joint pain, extreme fatigue, low mood and bowel inflammation. As a natural healthcare practitioner, I had always tried to support my health through nutrition, herbs and complementary therapies. However, following the birth of my second child, my recovery wasn’t as straightforward as I had expected. Wanting to understand what was happening, I decided to have a thorough health MOT, working alongside both my naturopath and GP. One of the key findings was that my vitamin D levels were clinically deficient. Vitamin D plays an important role in calcium absorption, bone health, muscle function and immune system function. Research has also explored its relationship with mood and inflammation, although the links are complex and the evidence is still evolving. There is ongoing discussion about what constitutes an optimal vitamin D level, particularly between conventional and functional medicine. While some practitioners advocate higher target levels, there is no universally agreed optimal range for every individual. A result also needs to be interpreted in the context of the laboratory reference range, your symptoms and your overall health. If you are experiencing any of the below symptoms seek appropriate medical care but also consider checking your vitamin D levels. Persistent fatigue Muscle aches, weakness or pains Bone pain or tenderness Low mood Slow wound healing Vitamin D & your health Vitamin D is a fat-soluble vitamin that supports many vital functions in the body. Ideally, we obtain most of our vitamin D from sunlight, with smaller amounts from food. When UVB rays reach the skin, they trigger the production of cholecalciferol (vitamin D3), the precursor to the active form of vitamin D known as calcitriol. However, living in the northern hemisphere can make it difficult to produce enough vitamin D, particularly during the long, dark winter months when sunlight is insufficient. Our vitamin D production can also be influenced by how much time we spend outdoors, clothing and sunscreen use. How much sunlight do we need? The amount of sunlight needed to produce vitamin D varies depending on skin tone, time of year, time of day and how much skin is exposed. Fairer skin generally produces vitamin D more quickly, while darker skin contains more melanin, which reduces vitamin D production. In the UK, sunlight is generally insufficient for vitamin D production during autumn and winter. During spring and summer, short periods outdoors may help maintain vitamin D levels, but there is no single exposure time that works for everyone and it can be a fine line between exposing your skin to sunlight and protecting it at the same time. Why is Vitamin D important? Vitamin D plays a vital role in many processes throughout the body. Vitamin D receptors are found in numerous tissues, and the vitamin influences the activity of genes involved in a wide range of biological functions. Bone health: Vitamin D helps the body absorb calcium from the intestines, supporting healthy bones, teeth and normal bone mineralisation. Immune function: Vitamin D helps regulate immune responses, including the activity of immune cells and the production of antimicrobial substances that help defend the body against infection. Gut health: Vitamin D helps maintain the intestinal barrier and influences immune activity in the gut. Research into its relationship with the gut microbiome is ongoing. Brain health and mood: Vitamin D receptors are found in areas of the brain involved in mood regulation. Low vitamin D levels have been associated with depression and fatigue, although this does not necessarily mean deficiency is the cause, it may indicate that maintaining adequate vitamin D levels form a wider part of the picture when supporting overall health and wellbeing.