When you drink your coffee matters, study finds

People who drink coffee in the morning are 20 percent less likely to have metabolic syndrome than those who drink no coffee at all, according to a new study.

A research team led by Maoqi Shen of the Department of Cardiovascular Medicine at the Second Xiangya Hospital of Central South University in China analyzed the relationship between coffee consumption timing and metabolic syndrome in American adults, the Korea Food Communication Forum (KOFRUM) said Tuesday.

The study is a cross-sectional observational study comparing coffee-drinking habits and health status at a single point in time. It does not establish a causal relationship — that morning coffee directly prevents metabolic syndrome, or that afternoon and evening coffee harms metabolic health. The researchers also noted that coffee type, whether sugar or cream was added, and changes in drinking habits over time may not have been fully accounted for.

The research team analyzed dietary data from 11,632 adults aged 20 and older who participated in the US National Health and Nutrition Examination Survey between 2003 and 2018. Participants were divided into two groups — "morning-concentrated" drinkers and "all-day spread" drinkers — based on when they consumed coffee. Their rates of metabolic syndrome were then compared with those of non-coffee drinkers.

Morning-concentrated coffee drinkers were 20 percent less likely to have metabolic syndrome than non-drinkers. The association held even after adjusting for factors that could influence the results, including sex, age, income, smoking, alcohol consumption, exercise, sleep, diet quality and total caloric intake.

By contrast, those who spread their coffee consumption across multiple times of day showed no significant difference in metabolic syndrome prevalence compared with non-drinkers.

The researchers suggested that the metabolic effects of bioactive compounds in coffee — such as caffeine and polyphenols — may interact with the body's circadian rhythm. Because late-day caffeine intake can affect sleep and the biological clock, they said it is worth considering not only total coffee consumption but also the time of day it is consumed.