What does it mean if...

[gmesko]

I created a model with life expectancy as dependent and obesity, salary, % that workout, %female
and I get results like
Coefficient
Salary 8.28
Obesity -.00689
Exercise .03343
Obese -.-689004

However if I include % of smokers as a variable, the signs of the coefficients change and don't make sense anymore. For example I would get

Salary -1.58
Obesisty7 .002334
Exercise .033434
Obese .002225
Smokers -0.17787

Which is basically saying that those who make more live less years, and if you are obese you will live longer

Why would adding that varible change the signs, and how can I resolve it