Because deterioration starts out so slowly, people usually do not begin to notice there has been any decline until they reach their late 30s. A few fortunate ones don't notice it until their 40s. A few (usually) dishonest ones claim no losses into their 50s but they are almost inevitably lying, either to you or to themselves, or both. Though it might be wisest to begin combating the aging process at age 19, practically speaking, no one is going to start spending substantial money on food supplements until they actually notice significant lost function. For non-athletes this point usually comes when function has dropped to about 90 percent of what it was in our youth. If they're lucky what people usually notice with the beginnings of middle age is an increasing inability for their bodies to tolerate insults such as a night on the town or a big meal. Or they may begin to get colds that just won't seem to go away. Or they may begin coming home after work so tired that they can hardly stay awake and begin falling asleep in their Lazy Boy recliner in front of the TV even before prime time. If they're not so lucky they'll begin suffering the initial twinges of a non-life-threatening chronic condition like arthritis. The thinnest line demonstrates the worst possible life from a purely physical point of view, where a person started out life with significantly lowered function, lost quite a bit more and then hung on to life for many years without the mercy of death. If one can postpone the deterioration of aging, they extend and hopefully square the curve (retard loss of function until later and then have the loss occur more rapidly). Someone whose lifetime function resembled a "square curve"(the thickest, topmost line) would experience little or no deterioration until the very end and then would lose function precipitously. At this point we do not know how to eliminate the deterioration but we do know how to slow it down, living longer and feeling better, at least to a point close to the very end. Vitamin supplements can actually slow or even to a degree, reverse, the aging process. However, to accomplish that task, they have to be taken in amounts far greater than so-called minimum daily requirements, using vitamins as though they were drugs, a therapeutic approach to changing body chemistry profiles and making them resemble a younger body. For example, research gerontologists like Walford reason that if pantothenic acid (vitamin B5), in fairly substantial (but quite safe) doses can extend the life and improve the function of old rats, there is every indication that it will do a similar job on humans. Medical researchers and research gerontologists have noticed that many other vitamin and vitamin-like substances have similar effects on laboratory animals.