Major health insurance companies own nearly $4.5 billion worth of stock in tobacco companies, according to a Harvard University study. It kinda makes sense: health insurers know tobacco sickens people, and so as long as people are smoking, why not profit from the killer? It’s what David Himmelstein, a co-author of the study, calls “the combined taxidermist and veterinarian approach: either way you get your dog back.”

The largest tobacco investor on the list, the 160-year old Prudential company with branches in the US and the UK, has more than $1.5 billion invested in tobacco stocks. The runner-up was Toronto-based Sun Life Financial, which apparently holds over $1 billion in Philip Morris (Altria) and other tobacco stocks. In total, seven companies that sell life, health, disability, or long-term care insurance, have major holdings in tobacco stock.

Why is it a big deal? “If you own a billion dollars [of tobacco stock], then you don’t want to see it go down,” says Himmelstein, “You are less likely to join anti-tobacco coalitions, endorse anti-tobacco legislation, basically, anything most health companies would want to participate in.”

This is something to keep in mind this summer as Congress debates health care reform. Mandating health insurance using commercial, for-profit insurers may not be in our best interests.