Nocturnal workers may have predisposition to eat more

A new study conducted by Brazilian scientists suggests that nocturnal workers present alterations in hormonal functions that leave them predisposed to eat more, gain weight and develop metabolic syndrome.

By Fábio de Castro

Agência FAPESP – A new study conducted by Brazilian scientists suggests that nocturnal workers present alterations in hormonal functions that leave them predisposed to eat more, gain weight and develop metabolic syndrome – a set of cardiovascular risk factors that includes hyperglycemia, hypertension, obesity and an increase in waistline circumference.

International scientific literature had already shown that nocturnal workers have a greater tendency to gain weight, in addition to the risk of presenting cardiovascular disease and other indicators of metabolic syndrome.

Changes in diet associated with nocturnal work – including increased caloric values and variations in the schedule and number of meals – have been indicated as the most probable explanations for this phenomenon.

Studying the biological mechanisms that could be behind these behavioral changes, a group of researchers at Universidade Estadual de Campinas (Unicamp) discovered that nocturnal workers present alterations in hormonal functions that regulate satiation – the sensation of being satisfied after a meal – which could lead to weight gain.

The study coordinated by Bruno Geloneze Neto, of the Unicamp Medical Sciences School received FAPESP funding through the Regular Research Award program. “Our conclusion is that hormone function in the regulation of satiation suffers alterations in people who work at night,” Geloneze explains to Agência FAPESP.

According to Geloneze, the study was conducted with a group of 24 women, half of which working the night shift and the other 12 the day shift at Unicamp’s Hospital das Clínicas. All had body mass indices between 25 and 35.

“We studied the hormonal mechanisms linked to satiation and not the behavioral differences. We were careful to work only with people of the same sex and with similar standards of weight, physical activity, socioeconomic and cultural standards, as means of observing the differences related to the variable of work shift,” says Geloneze.

According to Geloneze, the international literature highlights that nocturnal workers have a higher risk of gaining weight and developing cardiovascular disease, associating this phenomenon to an increase in caloric consumption.

But till now, the studies had not revealed whether this increase occurs due to the stress caused by the break in the biological rhythm as a result of working at night or because of a purely behavioral factor: as if a lack of stimulus in the nocturnal period prompted individuals to eat more – which scientists suspect is a myth. 

“We sought to investigate one aspect for which there is not much data in the literature: how do the gastrointestinal hormones that control hunger and satiation behave? Some studies show that there is an alteration in the levels of leptin – a hormone related to the degree of adiposity – in nocturnal workers. But it was unknown whether leptin changed as a result of the weight gain or if it was the cause,” he explained.

The volunteers were submitted to a standard dietary test, which consisted of ingesting 515 calories, with a hyperprotein and hyperlipidic diet. The nocturnal workers were tested during the day on their days off. The daytime workers were tested during their normal schedules.

“After eating, we studied their production of insulin and three GLP-1 and PY-B36 hormones – both with anorexigenic action,- from ghrelin, a hormone produced in the stomach which stimulates hunger, and xenin, a hormone that inhibits hunger,” he explained.

A little before their standard meal, the ghrelin levels presented spikes, while the other three hormones remained at lower levels. After the meal, for a period of three hours, the GLP-1, PY-B36 and xenin rose and ghrelin dropped.

“In individuals that worked at night, the GLP-1 and PY-B36 levels were similar to those of daytime workers. But we identified a change in the production of ghrelin among nocturnal workers,” he said. Normally, according to Geloneze, after a meal, ghrelin production drops below the baseline. Among the nocturnal workers, ghrelin suppression did not occur after the meal.

“The other difference that we observed occurred in relation to xenin. This hormone normally increases after the meal, contributing to satiation. But in the women who work at night, production of xenin did not rise,” said the researchers.

From a clinical standpoint, there was discrete difference in the quantity of calories ingested, of roughly 10%. Although the nocturnal workers had the same levels of body mass index, they had a little higher concentration of fat in the abdomen.

“When we talk about treatment of obesity, we need to take into consideration that people’s conditions are very heterogeneous and a single therapeutic approach may not be enough. Now we know that nocturnal workers would need to have therapies focused on these subjacent mechanisms, such as, for example, drugs that modulate production of xenin and gherlin,” he affirmed.