Night owls -- people who prefer staying up late -- may have a higher risk of suffering from heart disease and type 2 diabetes than early risers, a study has found.
The first-ever international review of studies analysing whether being an early riser or a night owl can influence your health, researchers have uncovered a growing body of evidence indicating an increased risk of ill health in people with an evening preference as they have more erratic eating patterns and consume more unhealthy foods.
The human body runs on a 24-hour cycle which is regulated by our internal clock, which is known as a circadian rhythm, or chronotype.
This internal clock regulates many physical functions, such as telling you when to eat, sleep and wake. An individual's chronotype leads to people having a natural preference towards waking early or going to bed late.
The researchers found increasing evidence emerging from studies linking conditions such as heart disease and type 2 diabetes to people with the evening chronotype -- a natural preference for evenings.
People who go to bed later tend to have unhealthier diets, consuming more alcohol, sugars, caffeinated drinks and fast food than early risers.
They consistently report more erratic eating patterns as they miss breakfast and eat later in the day. Their diet contains less grains, rye and vegetables and they eat fewer, but larger, meals.
They also report higher levels of consumption of caffeinated beverages, sugar and snacks, than those with a morning preference, who eat slightly more fruit and vegetables per day.
This potentially explains why night owls have a higher risk of suffering from chronic disease.
Eating late in the day was also found to be linked to an increased risk of type 2 diabetes because the circadian rhythm influences the way glucose is metabolised in in the body.
Glucose levels should naturally decline throughout the day and reach their lowest point at night. However, as night owls often eat shortly before bed, their glucose levels are increased when they are about to sleep.
This could negatively affect metabolism as their body isn't following its normal biological process.
Every additional hour spent outdoors was associated with 30 minutes of 'advance sleep' and that the noise, ambient lighting and crowding of urban environments can make people in some areas more likely to have a morning or evening preference.
The researchers also found evidence that night owls would accumulate 'sleep debt' during the working week and would sleep longer at weekends to compensate for this, whereas early birds had smaller differences in their sleeping patterns across the week.
"We have found that your genes, ethnicity and gender determine the likelihood of you being a morning or evening type," said Suzana Almoosawi, Northumbria University in the UK.
"In adulthood, being an evening chronotype is associated with greater risk of heart disease and type 2 diabetes, and this may be potentially due to the poorer eating behaviour and diet of people with evening chronotype,
"Our review also found that people who have a poorer control of their diabetes are more likely to be evening types," she said.