Girls who frequently consume sugary drinks tend to start their menstrual periods earlier than girls who do not, according to new research from Harvard Medical School in Boston.
The study, published online today in Human Reproduction, one of the world’s leading reproductive medicine journals, is the first to look at the relation between sugar-sweetened drinks and the age at which girls have their first period.
Study method
Researchers followed 5,583 girls, aged 9-14 years between 1996 and 2001 and found that those who drank more than 1.5 servings of sugary drinks a day had their first period 2.7 months earlier than those who consumed two or fewer such drinks a week. The researchers said this effect was independent of the girls’ body mass index (BMI), height, total food intake and other lifestyle factors such as physical activity.
The girls in the study were part of the Growing up Today Study, which follows 16,875 children of Nurses’ Health Study II participants living in all 50 states of the US. At the time of joining the study none of the girls had started their periods; by the end of the study all but 3 per cent (159) had started menstruation. The researchers used questionnaires to ask the girls about their diet at several points during the study, including how frequently, on average, they drank a serving of different types of drinks: one can or glass of soda or diet soda (soda being carbonated drinks such as colas), one glass of non-carbonated fruit drinks (fruit mixes such as lemonade, punch and other non-carbonated fruit drinks), or one glass, can or bottle of sweetened ice tea. All of these drinks have sugar added to them in the form of sucrose, glucose, corn syrup etc, while the colas and iced tea also contain caffeine. The researchers also investigated diet sodas and fruit juice to assess the impact of artificially or naturally sweetened drinks.
Girls drinking sugar-sweetened drinks more likely to start period
Diet sodas and fruit juices were not associated with any difference in the age at which girls started their periods. However, at any age between nine and 18.5 years, girls who reported consuming more than 1.5 servings of sugar-sweetened drinks a day were, on average, 24 per cent more likely to start their first period in the next month relative to girls consuming two or fewer servings a week, taking into account factors that could affect the age of first menstruation, such as birth weight, physical activity, race or ethnicity, height, frequency of eating dinner together as a family, and family composition (whether or not a father or step-father lived at home).
The average age of the first period among girls consuming the most sugary drinks was 12.8 years, compared to 13 years for those drinking the least.
When the researchers adjusted their results to take account of BMI, the effect of sugary drink consumption on the age of onset of menstruation was still significant: girls consuming the most were 22 per cent more likely to start their first period in the next month compared to girls consuming the least.
Links between earlier periods and breast cancer later in life
The researchers said their findings were important not only because of the growing problem of childhood obesity in a number of developed countries, but also because starting periods earlier is linked to an increased risk of breast cancer later in life.
According to the researchers, a one-year decrease in age at menarche is estimated to increase the risk of breast cancer by 5 per cent, meaning a 2.7 month-decrease in age at menarche was likely to have “a modest impact” on breast cancer risk.
“Our study adds to increasing concern about the wide-spread consumption of sugar-sweetened drinks among children and adolescents in the USA and elsewhere,” said Karin Michels (ScD, PhD), Associate Professor at Harvard Medical School Boston, who led the research.
“The main concern is about childhood obesity, but our study suggests that age of first menstruation (menarche) occurred earlier, independently of body mass index, among girls with the highest consumption of drinks sweetened with added sugar,” Associate Professor Michels said. “These findings are important in the context of earlier puberty onset among girls, which has been observed in developed countries and for which the reason is largely unknown,” she said.
Sugary beverage consumption ‘can be modified’
In the paper, the researchers wrote that the “public health significance of sugar-sweetened beverage (SSB) consumption at age at menarche, and possibly breast cancer, should not be over-looked, since, unlike most other predictors of menarche, SSB consumption can be modified”.
“The amount of SSBs consumed by girls in our highest category of consumption, more than 1.5 servings per day, however, is likely low compared with consumption in certain other populations, in which we would expect an even more dramatic decrease in age at menarche,” the researchers wrote.
High glycemic index could be link to sex hormones
The researchers said that drinks with added sugar have a higher glycemic index than naturally sweetened drinks such as fruit juices, and high glycemic foods result in a rapid increase in insulin concentrations in the body.
Higher insulin concentrations can result in higher concentrations of sex hormones, and large alterations in the concentrations of these hormones circulating in the body has been linked to periods starting earlier. Greater caffeine intake has also been associated with earlier periods. However, the researchers found that total sugar or caffeine intake did not explain their results, and that it was the added sugar in drinks such as sodas that was the culprit. Greater BMI only partially explained the results and was not the main mediator.
“Our findings provide further support for public health efforts to reduce the consumption of sugary drinks,” Associate Professor Michels said.
Experts say further factors need to be analysed
Child medical experts have had a mixed reaction to the study, suggesting that further research needs to be undertaken to more fully understand the impact of sugar-sweetened drinks on health.
Professor Ieuan Hughes, Emeritus Professor of Paediatrics at the University of Cambridge said the median age of menarche in the study, 12.7 years, was “absolutely the population norm and has not changed for the past 40-50 years”.
“But the unadjusted sample in the study actually had a higher value ( 13.1) which ‘disappeared’ when a whole raft of adjustments were made based on the SSB intake at the lowest and highest end of the range,” Professor Hughes said. “How biologically relevant is a difference of 2.7 months?” he said.
Location and early childhood nutrition could also be factors
Professor Hughes also suggested the effect of migration and locality and parents’ occupations needed was not controlled for in the study, and could have some influence on the results.
“The authors admit that future studies should examine the impact of early childhood nutrition on menarche,” Professor Hughes said. “It seems to me that the observation in this study suggests that it is weight related so that the message is clear about the dangers of such sugary drinks. I think the reference to breast cancer is overly alarmist though,” he said.
Childhood height and weight could influence outcome
Dr Ken Ong, Programme Leader and Paediatric Endocrinologist, MRC Epidemiology Unit and University of Cambridge, said that the study was very large and “representative across the US” and that the findings were “strongly statistically significant”.
“From previous research we know that sugar-sweetened beverages (SSB) intake promotes weight gain, and that weight gain promotes early puberty in girls – so a ‘SSB-to-puberty’ link is expected (although not previously shown),” Dr Ong said. “The surprise here is the claim that the association is independent of childhood size – i.e. that there is a more direct effect of SSB on puberty. This is unexpected,” he said.
Dr Ong said the study’s main limitation was that crucial factors such as childhood height and weight were not measured in their study, but were self-reported by the families.
“Errors in this reporting could explain the lack of the expected role of weight/BMI in explaining the SSB-puberty link,” Dr Ong said.
“We do have causal evidence (from other studies) that SSB intake promotes weight gain in children – so clearly excessive SSB intakes should be avoided,” Dr Ong said. “We also know that rapid weight gain promotes early puberty, so reducing SSB might well help to avoid early puberty. But we don’t yet know if and how SSB might influence puberty directly, separate to body size,” he said.
