"IU" is a measurement common in pharmacology, and has to do with trying to standardize how much mass/volume of a substance will give a particular biological effect. The "/d" is per day.
In summary, the article is saying that, based on a meta analysis[1] of previous research, we have misunderstood or misreported some of these measurements. They suggest both the safe dosage and the effective dosage for Vitamin D should be much higher, and argue that this is a cheap and effective way of treating problems associated with Vitamin D deficiency.
"IU" is a measurement common in pharmacology, and has to do with trying to standardize how much mass/volume of a substance will give a particular biological effect. The "/d" is per day.
In summary, the article is saying that, based on a meta analysis[1] of previous research, we have misunderstood or misreported some of these measurements. They suggest both the safe dosage and the effective dosage for Vitamin D should be much higher, and argue that this is a cheap and effective way of treating problems associated with Vitamin D deficiency.
[1] https://en.wikipedia.org/wiki/Meta-analysis
(edited for spelling)