Comments by "Keit Hammleter" (@keithammleter3824) on "Why You Need Vitamin D | And How You Get It From the Sun" video.

  1. Unless you can put numbers on it, like how many minutes sun exposure you actually need per day, for given amounts of skin uncovered by clothing, there is no point in teaching it - it's in practice meaningless. Especially when school kids are strongly taught that sun exposure leads to skin cancer and they must be fully covered or covered in UV blocking cream at all times in the sun. How do you expect them to resolve this dilemma when even doctors don't know.
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  2. At the end you say you have covered everything. Nope. You missed out the most important item of information - just how much sun is needed. Here in Australia at least, doctors are taught that a lack of Vit D is just about impossible, due to our high ultraviolet levels from the sun - that's what they commonly tell patients anyway. But campaigns warning about skin cancer are run all the time. What would be of practical use would be to know just how much sun is needed to get sufficient Vit D. If only your arms are uncovered, how long in the sun do you need to be? If your legs are uncovered, presumably you need less time to make sufficient Vit D due to much greater exposed area. Is this in fact so? What if I spend 5 minutes in the sun, or 10 minutes, or 20 minutes? Is Vit D production directly proportional to exposure time, or is there a law of diminishing returns? Does Vit D production start instantly, or does the process take time to get going? How much time does it take to get going? Does 5 separate periods of 5 minutes in the sun make as much Vit D as one 25 minute session in the sun? Does Vid D production rise linearly with ultraviolet intensity, or is it power or sub-power relationship? Presumably production depends on skin temperature, as most biological reactions double in speed for each 10 C rise in temperature. Is skin temperature in practice a factor? Unless you can answer these questions, talking about getting Vit D from the sun is completely pointless. About as pointless as saying money brings happiness. How long is a piece of string?
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