What's the base chance? 20% is probably a meaningless difference. But this is why relative risk numbers are typically useless.From the research, the overall effect in the broad population was about a 20% reduction in the chance of contracting an acute respiratory tract infection. Now that might mean that people are on average slightly deficient, especially if the research was based on subjects mainly in the northern hemisphere or cold climates, but since most people wouldn't know if they are deficient, and/or sit inside all day this is not something to thumb your nose at. In people who are very deficient, typically the elderly (the highest risk group), the benefit is a 70% reduction in the chances they would otherwise have of contracting an acute respiratory infection. Based on this I'd say it's pretty compelling that you should take vitamin D unless you're outdoors all day, and especially if you're older.
There's no reason to believe someone living in a sunny location would need to be exposed to the sun all day. Especially if they're white.
