Dilution is the Solution (to Aging)
In the post on osteocalcin that I can never quite finish I paraphrased a review on the topic that suggested that undercarboxylated osteocalcin may be one of the anti-aging factors present in 'young blood'. Heterochronic parabioss experiments - wherein the circulatory systems of an old and a young mouse are joined - have shown rejuvenating effects for the old mouse and some age-promotion in the young. This has lead to speculation that there are youth-promoting factors in the blood of the younger mouse that provide benefit to the older mouse. However the Conboys and their research team, who pioneered heterochronic parabiosis experiments, have proposed that it is actually dilution of pro-aging factors that provides the age-reversing effects. They recently published an article [Mehdipour et al. 2020] showing dilution of the blood of an old mouse is sufficient for rejuvenation. From the article: "The above concept fits well with the age-imposed increase in systemic TGF-beta