I went all the way through to the summary, the main article is behind a paywall. The amount used in the studies was around 800IU. If you go outside in the summer in your swimming trunks or bikini for 15 minutes or so your body will generate 10,000 - 25,000IU. Your mileage will vary according to latitude and skin color. But the point is that the amount used in the studies was ridiculously small. I take 10,000IU per day and this article wont change my mind.