Can you have high cholesterol and still be thin and active?
Yes, and it is common enough that being slim is a poor reason to skip testing. A substantial component of cholesterol is genetically determined — familial hypercholesterolaemia affects roughly one in 250 people and produces high LDL from birth regardless of diet or fitness, yet is largely undiagnosed. Other causes in lean people include hypothyroidism, kidney disease and certain medications. The practical implication is that lipid screening should be based on age and family history rather than appearance, and a strong family history of early heart attacks is a specific reason to test earlier and look for a genetic cause.
Answers
Early heart attacks in the family being the flag is the practical takeaway. That history should trigger testing regardless of build.
Familial hypercholesterolaemia being largely undiagnosed is a genuine public health gap and one in 250 is not rare.