UCSF researchers compared levels of the stress hormone cortisol in 338 kindergartners whose families annual incomes ranged from less than 10,000 dollar to 200,000 dollar-plus. The research team found that the average cortisol level among 113 of low-income children who lived in poor neighborhoods reached the 75th percentile. But when they looked at cortisol levels in 32 low-income children living in better-quality neighborhoods, the average was in the 45th percentile, the researchers report in the May 8, 2018, issue of Psychosomatic Medicine.