Vitamin D
Vitamin D is often called the 'sunshine vitamin' because our bodies can produce it when skin is exposed to sunlight. In the UK, sunlight isn’t strong enough for much of the year, and many people struggle to maintain optimal levels through diet alone.
Vitamin D supports bone health, immune function, mood and overall wellbeing - but the right amount varies between individuals. Supplementation can be helpful, especially in winter, although not eveyone needs supplementation.
What vitamin D actually is
Vitamin D is a fat-soluble nutrient that the body synthesises when skin is exposed to UVB sunlight, and that is also found in some foods and supplements. Unlike most nutrients, vitamin D functions as both a nutrient and a hormone, with receptors throughout the body.
It plays a crucial role in:
calcium absorption
bone and teeth health
immune function
muscle function
mood regulation
There are two main forms:
Vitamin D2 (ergocalciferol) - found in some plant sources
Vitamin D3 (cholecalciferol) - the form our skin produces from sunlight, and typically the one used in supplements
Why do we take vitamin D supplements?
Vitamin D supplements are taken widely by people seeking general health support, bone health, immune function and mood, often based on awareness of deficiency prevalence in some populations. Many people take vitamin D without knowing their baseline status.
Because vitamin D affects many systems in the body, low levels can contribute to feeling run-down, low in mood or more susceptible to winter illnesses.
What large-scale research is showing
Vitamin D deficiency (serum 25-hydroxyvitamin D < 30 nmol/l) is genuinely associated with worse health outcomes for bone, immune function and other systems, and correction of severe deficiency is essential.
However, in trials supplementing people with adequate or borderline vitamin D levels, broad health benefits have not been consistently demonstrated. Large vitamin D supplementation trials have not prevented heart disease, cancer, or infection in general populations, though some analysis suggests potential benefits in people starting from deficiency.
For bone health, the effectiveness of supplementation depends on baseline vitamin D status, calcium intake and age.
The research also highlights that:
people living in northern climates often have low levels
deficiency is more common in individuals with darker skin tones
low levels are particularly common during autumn and winter
Supplementation is well researched, but it works best when tailored to individual needs, and ideally guided by blood testing where appropriate.
Where supplementation is appropriate
Vitamin D supplementation is most clearly evidence-based in people with documented deficiency, pregnant and breastfeeding individuals in some populations, older adults at risk of falls or bone loss, and those with limited sun exposure or darker skin in high-latitude regions. Testing baseline status before supplementing is sensible, as it allows for more targeted dosing.
Vitamin D may be useful to consider if you:
spend most of your time indoors
feel low in energy or mood during winter
live in the UK or another northern country
have limited dietary sources of vitamin D
follow a vegan or plant-based diet
cover your skin for cultural or personal reasons
have darker skin, which naturally reduces vitamin D synthesis
have low vitamin D on a blood test
People often notice improvements in energy, mood and overall wellbeing once levels are restored.
When context matters
The relationship between vitamin D and health is dose-dependent and context-dependent. Both deficiency and very high levels can cause problems. Supplementing without knowing baseline status or accounting for sun exposure, skin tone (which affects synthesis), diet and medications can result in either inadequate dosing or excess accumulation.
Although vitamin D is generally safe, caution is needed if:
you are taking medications that affect calcium levels
you have kidney disease
you have disorders of calcium metabolism
you are already using high-strength vitamin D supplements
you take multiple multivitamins or fortified products
Why broad supplementation is not supported by evidence
Supplementing people with already-adequate vitamin D status does not produce the health benefits sometimes implied in marketing. The relationship is not linear - more vitamin D does not equal more benefit once adequacy is reached.
Food-first and sun exposure support
Vitamin D is naturally present in fatty fish (salmon, mackerel), egg yolk, mushrooms exposed to sunlight, and fortified dairy or plant-based milk.
More substantially, regular sun exposure (without causing sun damage) - roughly 10–30 minutes of midday sun exposure several times weekly, depending on skin tone and latitude - allows the body to synthesise vitamin D.
For those unable to access adequate sun or food sources (pregnant individuals, older adults, those with darker skin in northern latitudes), supplementation may be appropriate, ideally with baseline testing to determine need.
Vitamin D health check
If you’re uncertain about vitamin D supplementation get in touch. We can arrange a vitamin D blood test and discuss the appropriate supplementation plan for you.
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