Vitamin D is one of the few supplements that public health bodies in many countries actively recommend, and for good reason: deficiency is genuinely common, particularly in regions with long, dark winters. Often called the "sunshine vitamin," vitamin D is made in your skin when exposed to sunlight, which is exactly why so many people run low. Here is what to know.
Why vitamin D matters
Vitamin D helps your body absorb calcium, making it essential for strong bones and teeth. It also plays roles in muscle function and immune health. Severe, prolonged deficiency can lead to soft, weak bones, while milder shortfalls are linked to fatigue and bone or muscle aches, though symptoms are often vague and easy to miss.
Common signs and symptoms
Vitamin D deficiency is frequently silent, which is part of why it goes undetected. When symptoms do appear, they tend to be non-specific.
- Persistent tiredness or low energy
- Bone pain or aching
- Muscle weakness or aches
- Frequent infections or feeling run-down
- Low mood, particularly in winter months
Symptoms overlap with many things
Fatigue and aches have countless causes. The only reliable way to know if you are deficient is a simple blood test, not guesswork.
Who is most at risk
Some groups are far more likely to be low and may benefit from routine supplementation, depending on local health guidance.
- People living in northern latitudes, especially in autumn and winter
- Those who spend little time outdoors or cover most of their skin
- People with darker skin tones, which produces vitamin D more slowly
- Older adults, whose skin makes less vitamin D
- People who are pregnant or breastfeeding
- Those with certain digestive conditions affecting absorption
Sources of vitamin D
Few foods naturally contain much vitamin D, which is why sunlight and, for many, supplements are important. Dietary sources can still contribute.
- Sunlight on bare skin, in moderation and balanced with sun safety
- Oily fish such as salmon, mackerel, and sardines
- Egg yolks
- Fortified foods like some milks, plant drinks, and cereals
Too much can harm
Very high doses of vitamin D over time can cause dangerous calcium build-up, leading to nausea, confusion, and kidney problems. Never take high-dose supplements without medical advice. For severe symptoms like confusion or persistent vomiting, call 911 (US/CA), 999 (UK), or 112 (EU).
What to do if you suspect deficiency
Rather than starting a high-dose supplement on a hunch, the smart first step is a blood test to confirm your level. Based on the result and your health, a clinician can recommend the right dose, which varies from person to person. Many people benefit from a standard maintenance dose through winter, but the specifics should be individualised.
Vitamin D is a rare case where supplementation is genuinely useful for many people, but more is not better and testing beats guessing. If you have symptoms, fall into a higher-risk group, or want to know your level, a verified doctor on iHealix can arrange testing and advise on a safe, appropriate dose for you.