Sam Jonas has psoriasis -- a skin condition that leaves red, scaly patches on his body.
"It can be very embarrassing," Jonas told Ivanhoe.
Several years ago, Jonas also had a heart attack. He never knew the two conditions were related, until he found out they're shadow diseases.
"There are diseases that exist that, for some reason or another, seem to follow one another like a shadow," David Ancona, M.D., F.A.C.C., a cardiologist at Memorial Hospital West in Pembroke Pines, Fla., explained.
A serious case of psoriasis could double your risk of heart attack. Some other shadow diseases include asthma and mental problems. Those with the breathing problem are more than twice as likely to suffer depression or anxiety.
Another condition that's often followed closely by another are migraines. Those who get one migraine a month are 50 percent more likely to have a heart attack. Weekly migraines triple your risk of stroke.
Also, those with three of the five markers of metabolic syndrome -- a disease that affects 47 million americans -- are 70 percent more likely to get kidney stones.
In addition, a recent study of women shows hypertension doubles your diabetes risk, regardless of your body mass index.