Vitamin D: More Than a Sunshine Vitamin
Vitamin D is often associated with sunlight and bone health, but biologically it behaves more like a hormone than a conventional vitamin, influencing several systems throughout the body. It helps regulate calcium and phosphate metabolism, which supports bone mineralisation, muscle contraction, nerve signalling and normal cardiac function. Skeletal muscle contains vitamin D receptors, and low vitamin D status is associated with poorer muscle function, particularly in older adults, though that does not mean extra vitamin D automatically improves strength in someone already sufficient. Winter, indoor lifestyles, darker skin pigmentation and limited sun exposure can all increase the risk of low vitamin D status. Food sources include oily fish, egg yolks, fortified dairy and plant milks, and some mushrooms. Vitamin D is fat soluble, and excessive supplementation can lead to dangerously high calcium concentrations, so supplementation should be sensible and, where deficiency is suspected, guided by appropriate medical advice.
Vitamin D is often associated with sunlight and bone health, but biologically it behaves more like a hormone than a conventional vitamin. It influences several systems throughout the body.
Why is vitamin D important
Vitamin D helps regulate calcium and phosphate metabolism. Calcium is essential for bone mineralisation, muscle contraction, nerve signalling and normal cardiac function. Inadequate vitamin D can reduce calcium absorption and compromise bone health over time.
Vitamin D and muscle
Skeletal muscle contains vitamin D receptors. Vitamin D is involved in neuromuscular function and calcium handling.
Low vitamin D status is associated with poorer muscle function and physical performance, particularly in older adults. That does not mean extra vitamin D automatically improves strength in someone who is already sufficient. The important goal is to avoid deficiency.
Vitamin D and immunity
Vitamin D receptors are present on immune cells, and vitamin D helps regulate aspects of both innate and adaptive immunity. It is part of normal immune function, not a cure-all for infection.
Where do we get it
The major natural source is UVB exposure to the skin. Food sources include oily fish, egg yolks, fortified dairy products, fortified plant milks and some mushrooms.
During winter, UVB exposure can be lower. People who spend most of the day indoors, cover most of their skin, have darker skin pigmentation or have limited sun exposure may be at greater risk of low vitamin D status.
Can you take too much
Yes. Vitamin D is fat soluble. Excessive supplementation can lead to dangerously high calcium concentrations.
Supplementation should therefore be sensible and, where deficiency is suspected, guided by appropriate medical advice or testing.
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Frequently asked questions
Why is vitamin D described as behaving like a hormone?
Vitamin D helps regulate calcium and phosphate metabolism, which is essential for bone mineralisation, muscle contraction, nerve signalling and normal cardiac function. That broad, receptor-based influence throughout the body is closer to how a hormone works than how a typical dietary vitamin works.
Does taking vitamin D supplements improve athletic performance?
Low vitamin D status is associated with poorer muscle function and physical performance, particularly in older adults. That does not mean extra vitamin D automatically improves strength in someone who is already sufficient. The important goal is to avoid deficiency.
Can you take too much vitamin D?
Yes. Vitamin D is fat soluble, and excessive supplementation can lead to dangerously high calcium concentrations. Supplementation should be sensible and, where deficiency is suspected, guided by appropriate medical advice or testing.
Sources
- National Institutes of Health, Office of Dietary Supplements (2024). Vitamin D: fact sheet for health professionals. ods.od.nih.gov/factsheets/VitaminD-HealthProfessional
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