In the Bible, we find the command that all male children be circumcised on the 8th day after birth: "This is my covenant between me and you and your descendants after you that you shall keep: every male among you shall be circumcised. And you shall circumcise the flesh of your foreskin, and this shall be a sign of the covenant between me and you. And every male among you, when he is eight days old, shall be circumcised in all your generations; he who was born in your house or bought for money from any stranger, who is not of your offspring" (Genesis 17:10-12).
This commandment was written about 4000 years ago, and medicine was not nearly as developed as it is today.
Why did God order the circumcision of Abraham's male descendants on the eighth day? Why not sooner or later? Why did it have to be the eighth day?
It is rational and reasonable to ask these questions after reading the verses about circumcision on the eighth day.
In the 1930s, Danish researcher Henrik Dam and American researcher Edward Adelbert Doisy discovered what is needed for blood to clot.
Namely, the human body has 2 elements for blood clotting. One of them is called vitamin K. Vitamin K is not produced in the body until the 5th or 7th day after birth. Another clotting factor that is essential is called prothrombin. Prothrombin surprisingly builds up to 30% of normal by day 3 of life and then, with apparent consequence, peaks at 110% just on day 8, just before leveling off at 100% of normal.
For these discoveries, Dam and Doisy received the Nobel Prize in Physiology or Medicine in 1943. If vitamin K is not present in a large dose on the eighth day when the boy is circumcised, the boy will bleed to death. The reason why God established exactly the eighth day for circumcision is that vitamin K as well as prothrombin in a newborn reach its peak at the age of 8 days - then the child will bleed the least and the blood will clot the fastest.
