Breast cancer is more common among women who have never given birth… which would suggest that women who have largely or complete abstained from intercourse with men (nuns and lesbians, for instance) probably have higher instances of breast cancer than most women.
But at the same time, they’d have far fewer (if any) STDs.
I don’t mean to be contrary, but isn’t the question as stated an oxymoron?
No two things that are inversely correlated can be unrelated, by definition. If two things have an inverse correlation, they are by definition related. Inversely. That’s what correlation means.
I sort of get that gist that maybe we’re talking (though never so stated) of a causal relationship, but I really think this question would need to have ‘unrelated’ better defined in order to get factual answers.
I guess I read the question to mean “otherwise unrelated”.
I think OP was trying to exclude things like cowpox/smallpox.
But your way works, too. Just ignore all posts after OP. 
Try to turn the semantics radar off for a moment. Some of you are so busy arguing
over the identification of a tree (the meaning of a single word), you are missing
the forest (the intent of the question).
I understand the necessity of clear and unambigous questions and answers here, but
sometimes in the quest for such, some of you tend to be over zealous in dismissing
another’s post.
Right. It’s the best known example of heterozygote advantage. There are others, as discussed on that page.
Oddly, though, when men get the “women’s diseases” like breast cancer and MS, they usually get far more severe cases.
Anecdotal, I know. Maybe because nobody considers the diagnosis until the diseases are advanced?
The Unifying Diagnosis is one holy grail of medicine. Medical students have to be reminded that you can get ticks AND fleas.
My question was more about diseases with unknown etiologies and if the underlying processes could be understood by looking at diseases with inverse correlations. Schizophrenia could have an immune or autoimmune component due to the correlation with RA.
Didn’t they use infection with malaria (Malariotherapy) against syphilis in the days before antibiotics? I would think there would be an inverse correlation there.
Some time ago I read that Hansen’s disease (AKA leprosy) and tuberculosis are caused by closely-related bacteria, and that populations that have one of the diseases tend not to have the other.
Does HIV and later AIDS provide protection from anaphylaxis?