People who take vitamins may be perceived as healthier, but new research finds those people often engage in decidedly unhealthy habits -- possibly thinking the vitamins will make up for it.

A study in Taiwan discovered smokers who take vitamins smoked twice as much on average, and supplement-takers also made poorer food choices. Worse yet, the vitamin group was more likely to engage in risky behavior such as casual sex and binge drinking.

While research has shown some vitamins to be beneficial -- women of childbearing age might benefit from iron supplements, for example -- other studies show taking a multivitamin to have no health benefit whatsoever. For smokers, vitamin E and beta-carotene supplements could even increase the risk of getting cancer.

Studies on these types of supplements are often contradictory depending on who's studied and where, but one thing researchers can say for sure is that the rise in supplement use in the US has not resulted in lowered rates of obesity, diabetes, heart disease, osteoporosis or other chronic diseases.