Goleman relates the rocky relationship between the Russian novelist Leo Tolstoy and his wife, Sonya. Right before their wedding, Leo shared with her some of his diary entries, which detailed how he’d had an illegitimate child with a local woman. Heartbroken, Sonya vowed to “poison his life.” Life for both of them became angry and mistrustful, and neither felt safe or loved in their own home. Sonya stated in her diary that Leo’s cruelty would shorten her life. Goleman wonders whether this could be true: whether epigenetic factors like a toxic relationship can affect health and curtail life. He states that at least the inverse has proven to be true: Loving relationships extend life and promote health. Goleman provides anecdotes showing that in apes as well as humans, stressful, toxic relationships raise cortisol levels and thus negatively affect health. Even having a dismissive or insulting boss can affect health for the worse. Goleman also provides examples of a study in which people were exposed to the common cold and quarantined to see if they would develop symptoms. Those with toxic relationships were more likely to catch the cold, and those with healthy relationships were more likely to resist it.

Goleman points to another study that shows that the stress of caregiving for a chronically or terminally ill partner, parent, or child can have significant negative effects on the caregiver’s health, especially if they are caregiving in relative social isolation.