But in the background, a quieter scientific discussion has questioned whether social media is doing much harm at all. While a few researchers have claimed that digital technology is a powerful, causal factor in the rising rates of mental health problems, others have countered that the risk of harm for most teenagers is tiny — about the equivalent influence on well-being as wearing eyeglasses or regularly eating potatoes, one group calculated.

Now, the authors of the eyeglass paper have published a large, multiyear study providing what independent experts said was an unusually granular and rigorous look at the relationship between social media and adolescents’ feelings about life.

Analyzing survey responses of more than 84,000 people of all ages in Britain, the researchers identified two distinct periods of adolescence when heavy use of social media spurred lower ratings of “life satisfaction”: first around puberty — ages 11 to 13 for girls, and 14 to 15 for boys — and then again for both sexes around age 19.