High cholesterol is often thought of as a problem for people who are overweight, older or living on an unhealthy diet – but the reality is far less straightforward.Because it rarely causes symptoms, raised cholesterol can go undetected for years, quietly increasing the risk of heart attack, stroke and other forms of cardiovascular disease - even in those who appear to be slim and 'healthy'.These conditions remain the leading cause of death and disability in the UK and are responsible for around 170,000 deaths each year.Now, experts are warning that even 'healthy' people must be aware of their level of cholesterol - which is a fatty substance that builds up in the blood vessels. 'Your cholesterol levels won't automatically be "fine" because you are slim, exercise regularly and eat healthily,' says Dr Zoe Astroulakis, consultant cardiologist from New Victoria Hospital in London.'You cannot tell what your blood cholesterol is without a blood test. You may have had high cholesterol levels all your life, and yet wouldn’t show any signs of it.'But there are risk factors that could prove to be a red flag, and are a reason to get tested, according to Dr Astroulakis.Here, she outlines the exact family history you need to watch out for, as well as the signs that have nothing to do with your weight, shape or levels of body fat.