I think it's more that being overweight is a major cause of sleep apnea. It's not the only one, of course, but definitely one of the more prevelant. Sleep apnea can also cause heart problems if left untreated for a long time.
Losing weight should help with both sleep apnea and diabetes prevention. My sister, who has lost over 80 lbs was able to give up her C-Pap machine.