A 2016 systematic review published in the journal Heart found that loneliness and social isolation raise your risk of heart attack by 29% and stroke by 32%—numbers comparable to the effects of light smoking or obesity. Researchers analyzed data from 23 studies involving over 181,000 adults, tracking heart attacks, strokes, angina, and cardiovascular deaths.

A 2013 review from the University of Toronto (Frontiers in Genetics) reveals how smoking alters your genes—not by mutation, but by changing their “on/off” settings via DNA methylation. This epigenetic shift can silence protective genes or activate harmful ones, linking smoking to cancer, heart disease, obesity, and even long-term issues in children exposed in the womb.