Vitamin C, evolution, and alternative medicine

Sometimes an evolutionary way of thinking could save us a lot of effort. There have been claims made for 50 years that large doses of vitamins, especially vitamin C, are good for you. There have been many studies done and they all show that there is no health benefit to large doses of any vitamins. In fact, more recent studies indicate that vitamin supplements harm your health and increase the chances of death.

That should not be surprising if we had some evolutionary background. Most mammals do not need any vitamin C in their diet at all, because they are able to synthesize it in their own cells. Primates (including humans) have lost this ability. One of the enzymes for making vitamin C has been mutated into a non functional state. Presumably, this is because primates get enough vitamin C in their diets so they do not need to make their own.

If large amounts of vitamin C were healthy, why would we have lost the ability to make it? If anything, evolution should have made the enzymes more active rather than inactive. The fact that mutations for inactivating vitamin C have been fixed means there was no selective pressure to maintain it--there was no harmful effect on the health of our ancestors.

Many alternative health claims are like this. Claims that our colons are filled with toxins that need to be flushed don't make sense. Why would evolution maintain our colons, or not make them flush more often?

We have to be careful with this logic. It is incorrect to think that evolution is always perfect. Sometimes evolution produces a messy way of doing things, some things aren't adaptations, and sometimes we are adapted to conditions that existed 50,000 years ago but no longer apply today. We still should do the studies to determine if vitamins help or hinder. But evolution can greatly increase the prior probability of a claim and help us to determine which claims are more worth pursuing.