It's difficult enough to deal with just one chronic disease and then you add another, often more serious one on top of it. Researchers are learning more and more about why two diseases that don't seem to be related at all travel in pairs. Here are some common shadow diseases that you need to know about. Doctor David Ancona says psoriasis can double the risk of a heart attack. One study showed women with endometriosis are 62% more likely to develop melanoma. Having just one migraine a month gives you a 50% higher risk of a heart attack. Having one a week gives you four-times the risk of a stroke. And having three of the five traits linked to metabolic syndrome ups the risk of kidney stones. Having either psoriasis or insomnia increases the chance of developing diabetes. And research shows nearly 50% of people with asthma also have a psychological condition like depression.