I walk for 30 minutes a day in direct sunlight. If I do this for a year (been 5 months so far) do I not need to worry about vitamin d intake? I am also a healthy young male in my 20’s
As others have pointed out, it depends on time of year and where you live. Far north, e.g. Canada, the U.K, Scandinavia the sun won't give you any Vitamin D at all for roughly six months of the year.
I’ve been using the DMinder app (not affiliated in any way and it’s totally free) to estimate how much vitamin D I’ve been getting. You input how overcast it is and what percent of your skin is exposed and then it uses your skin tone (input at setup), latitude, altitude, and time of day and it’ll track a rough estimate of how much vitamin D you’ve produced while you’re outside.
There’s also “Quick and Easy Screening for Vitamin D Deficiency in Adults”[1] which has a quick and dirty formula in Table 2 to help assess your risk of deficiency without a blood test.
Can’t find a citation at the moment, but it also depends on what part of your body is exposed. Just resting your forearm on an open car window won’t do it. You have to expose your torso mid-day IIRC.
Just as a pure speculation (I am not specialized in this area) I find it a little bit odd that forearm is not enough as I find it is the most common area exposed to sun by people at least in the last 100.000 years.
So I am wondering how come in this case selection did not chose those whose forearms can produce a lot of Vitamin D as it was probably the most exposed part to the sun.
Don't forget that many people used to bathe outside for many millenia. But I too would be interested in how clothing through generations have put selective pressures on humans, if any.