An 89-year-old retired businessman died from an “overdose” of Vitamin D supplements that did not warn about the risks of excessive intake.
David Mitchener from Oxted, Surrey, reportedly had fatally high levels of Vitamin D when he was brought to the East Surrey Hospital last year in May and was suffering from hypercalcaemia – a build-up of calcium in the body associated with taking too much vitamin D.
He died ten days later.
Vitamin D synthesis with sun on skin doesn't just convert all sunlight into vitamin D. Your body will stop synthesizing it at a certain point. It's not possible to overdose from sunlight.
I'm not saying that it's possible to overdose on vitamin D synthesised by exposure to sunlight, I'm just saying that I'm unconvinced that exposure to sunlight is in itself sufficient to meet vitamin D needs without dietary intake (especially for people who live a modern lifestyle where they don't necessarily get a lot of sun exposure).