Cholesterol is a waxy substance necessary to life. Our bodies themselves produce cholesterol. It is necessary for production of hormones and vitamin D to keep every cell healthy. There is good fat or HDL cholesterol and bad fat or LDL cholesterol. High levels of LDL cholesterol narrow the blood vessels which in turn lead to heart disease or stroke.
In a healthy person HDL cholesterol level must be greater than 45mg/dl and LDL cholesterol level below 150mg/dl.
The cholesterol level seems to depend on several factors such as genetic, age, lifestyle, exercise, body weight, diet, alcohol intake, smoking, and stress. Consumption of greater amounts of any fat than required leads to an increase in body weight. Being overweight increases the risk of increase of cholesterol level and cardiovascular disease as well. So, the over weight is the main cause for your friend’s cholesterol level.
Again we can not say that thin people can never have cardiovascular/ cholesterol issues. Though they do not come under body weight, but other factors may affect to their cholesterol level, take alcohol for example. Over drinking has bad impact on liver function and it is to be noted that liver make most of the HDL cholesterol.