Vitamins and minerals supply no energy, but their absence or shortage is where some of the most measurable, least controversial nutrition science exists. Deficiency diseases — scurvy (a vitamin C deficiency causing bleeding gums and fatigue), rickets (a vitamin D deficiency causing softened, weakened bones), goitre (an enlarged thyroid gland, from iodine deficiency), and pellagra (a niacin/vitamin B3 deficiency causing skin, gut, and neurological symptoms) — were largely solved by twentieth-century nutrition science and remain rare in food-secure populations, but suboptimal intake — short of overt deficiency — is still common.
The nutrients worth paying specific attention to
| Nutrient | Why it matters | At-risk groups |
|---|---|---|
| Vitamin D | Bone health, immune function; synthesised via sunlight exposure on skin. Low levels can show up as fatigue and bone or muscle aches | Anyone with limited sun exposure, darker skin tones, northern latitudes in winter[39][40] |
| Iron | Oxygen transport via haemoglobin (the protein in red blood cells that carries oxygen); deficiency causes fatigue and anaemia | Menstruating women, vegetarians/vegans, endurance athletes |
| Calcium | Bone mineralisation, muscle and nerve function. Deficiency is usually silent until bone density loss shows up later | Low dairy intake, post-menopausal women[40] |
| Iodine | Thyroid hormone production. Low intake can cause visible neck swelling (goitre) | Those avoiding iodised salt, dairy, and seafood |
| Vitamin B12 | Nerve function, red blood cell formation. Deficiency can cause tingling or numbness, brain fog, and fatigue | Vegans and vegetarians (plant foods contain negligible B12) |
| Folate | DNA synthesis; critical pre-conception and in early pregnancy. Low levels can cause fatigue and mouth sores | Women planning pregnancy or in the first trimester |
| Magnesium | Muscle and nerve function, energy metabolism. Low levels often show up as cramps or muscle twitches | Diets low in vegetables, legumes, nuts, and whole grains |
| Potassium | Blood pressure regulation, fluid balance. Low levels can cause muscle weakness or heart palpitations | Diets low in fruit and vegetables, high in processed food[41] |
Do you need a multivitamin?
If you eat a varied diet with enough calories, a daily multivitamin hasn't been shown to meaningfully cut disease risk or improve outcomes in large trials — think of it as insurance against minor gaps, not a performance or longevity boost. It makes more sense in specific situations: a restrictive diet, pregnancy, older age, or limited variety in what you eat. It's not a fix for an otherwise poor diet.