You don't have to sunbathe for hours to quickly replenish vitamin D deficiency in the summer months.
Vitamin D3 is a vitamin produced under the influence of the sun. There is not much of it in food - it is in egg yolks, salmon, tuna, beef liver or sardines, but you would have to eat these foods every day to make up for the shortage. Therefore, doctors suggest supplementation. And in the summer - exposure to the sun.
How long does it take to stay in the sun to replenish the shortage?
A 2010 study published in The Journal of Investigate Dermatology found that 13 minutes in a T-shirt and shorts 3 times a week for 6 weeks in the sun is enough to make up for a vitamin D3 deficiency.
So you should stay in the sun for at least 15 minutes a day and have at least 18 percent of the body surface exposed. Unfortunately - no filters are allowed then!
How much vitamin will we absorb? 30 minutes at noon gives you the same amount of vitamin D3 as taking 10-20 thousand units.
Source: At What Time Should One Go Out in the Sun?