For how we live.
When adults see a doctor for new fatigue, fewer than one in ten turn out to have clear physical disease. The common, treatable and often-missed exception is iron deficiency, which drains energy before it causes anaemia.
Feeling cold when others are comfortable can point to an under-active thyroid or iron-deficiency anaemia. Fingers and toes that turn white then blue in the cold are usually Raynaud's, a blood-vessel spasm.
In people who are iron-deficient without anaemia, supplements ease self-reported fatigue in trials — but do nothing for objective exercise capacity, and the benefit hinges on being iron-deficient, not just tired.
Milk is a useful source of calcium, protein and vitamin D for young children, but too much crowds out iron-rich food and can cause deficiency. Around two cups a day suits most toddlers.
Iron shortfall is the leading cause of anaemia in young children and is linked to poorer development. Yet the evidence that screening symptom-free toddlers or routinely supplementing them helps their brains is thin.
In one study of 62,685 women, iron deficiency prevalence ranged from 3% to 15% depending on the ferritin threshold. On treatment, a recent trial found alternate-day iron caused fewer side effects than daily dosing.