Smoking, Diabetes Mellitus, Thyroid Dysfunction, and a Variety of Drugs Have Potential Effects on Serum HDL-C Level.

A letter to editor is presented in response to article "The effect of residing altitude on levels of high-density lipoprotein cholesterol: A pilot study from the Omani Arab population" by N.B. Al Riyami and others, which appeared in a 2015 issue of the periodical.