The overlapping geography of cognitive ability and chronotype

Abstract

Chronotype and cognitive ability are two human phenotypes with an uneven geographic distribution due to both selective migration and causal environmental effects. In our study, we aimed to examine the relationship between geographic variables, cognitive ability and chronotype. We used a large anonymized sample (n = 25,700, mostly from the USA, UK, Canada and Australia) of dating site users to estimate chronotype and cognitive ability from questionnaire responses using item response theory. We matched each user to geographic coordinates and city size using the reported locations and geographic databases. In line with previous research we found that male sex, younger age, residence in a more populous locale, higher cognitive ability and more westward position within the same time zone were associated with later chronotype. Male sex, younger age, residence in a more populous locale, later chronotype and higher latitude were associated with higher cognitive ability, but the effect of population on chronotype and latitude on cognitive ability was only present in the USA. The relationship between age and chronotype was stronger in males, and the relationship between chronotype and cognitive ability was stronger in males and in older participants. Population density had an independent association with cognitive ability, but not chronotype. Our results confirm the uneven geographic distribution of chronotype and cognitive ability. These findings generalize across countries, but they are moderated by age and sex, suggesting both biological and cultural effects.

Daily rhythms, light exposure and social jetlag correlate with demographic characteristics and health in a nationally representative survey

“…In line with previous studies 11 , 12 , 14 , 53 we confirmed the observation that even within the same time zone with identical social time, people living further to the east and consequently experiencing earlier sunrises and sunsets report earlier chronotypes. The magnitude of this effect was 8.7 min per degree (111 km), which, extrapolated over the west–east span of Hungary of over 500 km, matches or even exceeds the maximal within-country difference in sunrise and sunset times, which is approximately 25 min.…”

“…Chronotype is associated with both normal and pathological variation in humans. Younger individuals, especially younger males, are on average characterized by a later chronotype 8 , 11 – 13 , as are people who live farther to the west within the same time zone and consequently experience sunsets at a later clock time 11 , 12 , 14 . A later chronotype is often associated with worse health outcomes across multiple health domains 15 , including both mental and physical health.…”

Daily rhythms, demographics and health: findings from a nationally representative survey

“…In line with previous studies 11,12,14,56 we confirmed the observation that even within the same time zone with identical social time, people living further to the east and consequently experiencing earlier sunrises and sunsets report earlier chronotypes. The magnitude of this effect was 8.7 minutes per degree (111 km), which, extrapolated over the west-east span of Hungary of over 500 km, matches or even exceeds the maximal within-country difference in sunrise and sunset times, which is approximately 25 minutes.…”

“…In line with previous Czech 11 and a multinational 47 study, but not with a global investigation 12 , we found that residence at northern latitudes is also associated with a later chronotype. While we cannot account for this unexpected finding, is not confounded by age, sex, education, income or population size, which were controlled for in statistical models.…”

“…Chronotype is associated with both normal and pathological variation in humans. Younger individuals, especially younger males, are on average characterized by a later chronotype 8,[11][12][13] , as are people who live farther to the west within the same time zone and consequently experience sunsets at a later clock time 11,12,14 . Besides evident sex-differences in preferred sleep-wake schedules/chronotypes, sexual orientation was shown to associate with anatomo-functional and phenotypic features of the master circadian clock and timing of activity and rest.…”