Volunteers at Boston Medical Center from a nonprofit called Health Leads are attempting to address the social and economic underpinnings of medical problems at a hospital where 75% of the patients use the state's low-income health insurance program, MassHealth. Health Leads, founded 16 years ago in Boston Medical's fifth-floor pediatric department as Project HEALTH, is a national endeavor working in pediatric and prenatal clinics, emergency rooms, and community health centers in six cities. Its mission: to help low-income families tackle the environmental and social issues that contribute to their health problems. More than 13,000 children visited BMC last year, and hospital officials said they expect the number to increase this year by about 20%. To respond to the growth, Health Leads officials in Boston said they plan to increase the number of volunteers, add more staff, and improve access to the patients' electronic records.