If you are one of the 133 million American grappling with a chronic illness like diabetes, asthma or heart disease, where do you turn for help managing your condition? Your employer may seem like an unlikely choice. Chronic conditions account for 25% of all medical costs, studies show, and an employee with a longstanding illness can mean higher health care expenses and lower productivity to company bean counters. Yet many firms have come to realize that it makes economic sense to help improve the health of workers who are the greatest users of medical services.