There is a tendency to throw ones hands up in exasperation at human health and fitness. “Chaos,” people cry. But it’s not random. It’s not chaos. Many processes are complex, and therefore vexing. But they are well-understood, if we take the time to breathe and reflect.
Fundamentally, where there are insufficient nutrients and over-abundant stressors, there will be a break down in health or fitness. This is the law. No exceptions. As random as it may seem, it’s in fact quite predictable. Many people will hold up singular statistical outlier anecdotes (ie - so-and-so ate and exercised “perfectly,” and then died of a massive heart attack) as evidence of chaos. It's not chaos. There is no perfect. Always, nutrients were insufficient and stressors were overwhelming.
Various modern health issues and risks are the focus of quackery and pseudoscience because a lot has changed in the last 100-200 years, and the simple mind wants to make a historical correlation into a causal connection. That said, recently, researchers at Brown discovered that Vitamin A has anti-skin cancer correlation: https://www.brown.edu/news/2019-07-31/skincancer
This wasn’t big new, by the way. Errant senescence of cells is really acutely understood. And this fat-soluble vitamin which was begun to be examined in the 1800s, has a well-defined role in immune function (therefore cancer management) and DNA transcription (therefore suppression of cancer cell proliferation). Our depleted soil leaves us with very little Vitamin A in foods which were once chock full of it. It isn’t random or chaos that getting insufficient nutrients raises risks and sufficiency lowers risks.It was entirely predictable that as we removed nutrients from our diets that there would be a higher incidence of certain cancers and diseases.
Human health and fitness follows physical laws.