Eating placenta has become really popular, especially since Mad Men star January Jones spoke to People Magazine about her own choice to have her son's placenta freeze dried and put into pill capsules. I have a lot of pregnant friends who plan on turning theirs into pills or consuming them in some other fashion. There are claims that it helps boost milk production, aid in healing, and alleviates postpartum depression among other things. Is there scientific evidence that this is true?
The eating of placenta is widespread in the mammalian kingdom - virtually all mammalian species do it (with humans, camels, llamas and alpacas being the notable exceptions).
I couldn't find studies looking at the affect of postpartum placenta eating in human females, however there are a couple out there looking at animals instead. Notably, there's a couple of studies in rats showing that placenta eating increases the analgesic effect of opiates.
On longer term benefits to the mother, it has been shown in dairy cows that placenta eating enables the mother to become fertile sooner.
I couldn't find any sound studies on whether placenta eating increases milk production, decreases the chances of depression or aids in healing. I have also heard that it's supposed to reduce the chance of the mother becoming anaemic (as it contains so much iron). However, there is a study in rats which shows that eating placenta does have an affect on hormone concentrations in the blood, so this would be a viable mechanism by which these effects occur.
Frustratingly, as I am more of a lurker than a contributor, I have been caught out by the spam filter and can only post two links. I've chosen the two I think most useful.
Edited to add:
Upon reading the dairy cow study closely, it seems that the cows were fed dried and ground placenta. This is interesting as it shows that the hormones in the placenta survive the drying process (so long as the hormones aren't denatured - they explicitly state they kept the temperature below 50 degrees C). This shows that there could be a basis for a woman having her placenta dried and put into capsules, however the cows ate up to 18kg of placenta over a period of a month. This is about 6 times the mass of a cow's placenta tissue, so is rather a lot! An average human placenta weights around 500g and so it could be assumed would contain a significantly smaller amount of hormone and the effects of eating one human placenta would probably be less.
Placenta does have beneficial properties.
We now know that placentas actually contain a whole host of bacteria — which is a good thing for baby's developing microbiome. Source: Before eating your placenta, read this study
However, there's no clinical evidence, that it helps to prevent or treat post-partum symptoms or PPD in women. Source
Empirical studies of human or animal consumption of human placentas were included. Editorial commentaries were excluded. Animal placentophagy studies were chosen based on their relevance to human practice. Ten articles (four human, six animal) were selected for inclusion. A minority of women in developed countries perceive placentophagy to reduce PPD risk and enhance recovery. Experimental animal research in support of pain reduction has not been applied in humans. Studies investigating placenta consumption for facilitating uterine contraction, resumption of normal cyclic estrogen cycle, and milk production are inconclusive. The health benefits and risks of placentophagy require further investigation of the retained contents of raw, cooked, and encapsulated placenta and its effects on the postpartum woman.
Animals eat their placenta in order not to give out the den and still hunger and restore the forces for the next day when the animal doesn't leave the cubs alone.