Don’t give vitamin D supplements to people who already have enough

For people who already have adequate vitamin D, taking supplements for 5 years yields identical rates of cancer, cardiovascular disease, and death as not taking them. Adults who rarely go outside and get no sunlight may take 400 IU daily, not exceeding 2,000 IU daily. Taking high doses actually accelerates volumetric bone loss and increases falls. Mere fatigue cannot be equated with vitamin D deficiency; if fatigued for weeks without clear reason, see a doctor.

Roughly 0.2 to 0.5 yuan per day, or 100 to 200 yuan per year. That’s not much money, but the real cost is the false sense of security it gives — the belief that you’ve already taken preventive steps.

The VITAL trial followed 25,871 participants who took 2,000 IU of vitamin D daily for a median 5.3 years: no statistically significant differences emerged across total invasive cancer (HR 0.96, 95% CI 0.88–1.06), major cardiovascular events (HR 0.97, 95% CI 0.85–1.12), all-cause mortality (HR 0.99, 95% CI 0.87–1.12), or depression incidence (HR 0.97, 95% CI 0.87–1.09). In the Australian D-Health trial of 21,315 adults aged 60 and older receiving 60,000 IU monthly for 5 years, all-cause mortality showed no significant difference (HR 1.04, 95% CI 0.93–1.18). Regarding megadoses, the VITAL fracture substudy (25,842 participants) found 2,000 IU/day did not lower total fractures (HR 0.98) or hip fractures (HR 1.01). The Calgary 3-year bone mineral density trial (400 vs 4,000 vs 10,000 IU daily) demonstrated that higher doses led to greater volumetric bone loss. In a Swiss randomized trial of women aged >=70 comparing 100 IU vs 24,000 IU vs 60,000 IU monthly, the high-dose arms experienced significantly more falls (HR 1.77) despite achieving target serum 25(OH)D levels. An Australian trial testing an annual bolus of 500,000 IU in older women observed a 15% increase in falls and 26% increase in fractures.

These trials specifically excluded people with proven severe clinical vitamin D deficiency, so findings apply to average individuals already getting sufficient intake. For individuals who rarely get sunlight exposure, national dietary guidelines recommend 400 IU daily, with a tolerable upper intake level of 2,000 IU daily for adults. Severe deficiency requires formal medical workup. Megadosing produces paradoxically poorer bone mineral outcomes and higher fall risks. Primary beneficiaries are yourself and your family.

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