Every autumn, UK headlines tell everyone to consider a vitamin D supplement. Read the sources, and the reason is simple: according to the NHS, from about late March to the end of September most people can make enough vitamin D from sunlight, but from October to early March there isn’t enough sunlight. Food Standards Scotland puts it in the same terms, encouraging everyone in Scotland to consider a supplement between October and March.
The US National Institutes of Health fact sheet I read is different. It gives recommended daily amounts by age, and doesn’t mention a seasonal supplement. That doesn’t mean one country is wrong. They’re different kinds of advice, and I haven’t found a source that explains how they relate.
All the sources agree on one thing: more is not better. The NHS gives upper limits, and warns that too much over a long time can cause hypercalcaemia. The NIH sheet says high levels are almost always caused by supplements, not sunshine.
Three caveats. The NHS page I read was last reviewed in 2020. The US sheet I could open was an archived 2021 copy. And the European figure I found came from a trade-news summary. Check the current pages, and ask a pharmacist or doctor if you take medicines, are pregnant, or are buying for a child.
My full guide has the details: more
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