Sugary soft drinks linked to earlier periods in girls

“Sugary drinks may cause menstruation to start earlier, study suggests,” reports The Guardian, reporting on a US study looking at the consumption of sugar-sweetened beverages (SSBs) in teenage girls.

This study included over 5,000 girls. It first assessed them when they were aged 9-14 years, asking them whether they had started their periods and assessing their consumption of SSBs. The girls were followed up annually.

The study found that girls in the highest consumption category (more than 1.5 SSB servings per day) were 22% more likely to start their period in the next month than girls in the lowest consumption category (two or fewer SSB servings per week). Girls in this highest consumption category started their periods at an average age of 12.8 years, which was 2.7 months earlier than girls in the lowest consumption category.

However, this study does not prove that SSB consumption is the direct cause of this difference, as many unmeasured health and lifestyle factors may be influencing the relationship.

One potential concern is that an early onset of menstruation (menarche) has been linked to an increased risk of some types of cancer, such as breast cancer. However, even if SSBs have a direct effect on menarche, cancer outcomes were not assessed by this study. It is uncertain whether the small difference seen, which is just a few months, would have any meaningful effect on later risk of breast cancer.

Overall, people should not be overly concerned, though the limitations of this study do not take away from the fact that SSBs are high in sugar and calories. Sugar can lead to tooth decay, and a high intake of sugar and calories can lead to obesity.

Where did the story come from?

The study was carried out by researchers from Harvard School of Public Health and Harvard Medical School, and was funded by the Breast Cancer Research Foundation, the National Institute of Environmental Health Sciences and National Institutes of Health, among other sources. The study was published in the peer-reviewed medical journal Human Reproduction on an open-access basis, so it is free to read online or download as a PDF.

The media correctly reported the association between fizzy drinks and earlier age of starting periods, but some headlines, such as The Daily Telegraph’s suggestion that such drinks “cause early puberty”, are unproven.

In addition, The Telegraph’s and the Daily Mirror’s headlines that the drinks “increase [sic] cancer risk in girls” may cause undue alarm. It is important to highlight that the study has not looked at cancer outcomes, either in girls or when they grow into women. This headline purely relates to the fact that the earlier age of starting periods is recognised as a risk factor – among many others – for cancers such as breast and endometrial (womb) cancer.

What kind of research was this?

This was an analysis of data collected in a prospective cohort study that aimed to see whether SSB consumption in girls is associated with the age when their periods start (menarche).

The researchers used participants of “The Growingup Today Study”, a prospective cohort study of children of participants in the US Nurses’ Health Study II. The researchers say how age at menarche is known to have decreased considerably in the Western world over the past couple of centuries. They say that the association of later menarche with calorie restriction and earlier menarche in children with a higher body mass index (BMI) supports the importance of nutritional factors. Previous studies are said to have investigated the link between protein intake and menarche, but the link with many other food groups remains unstudied. The researchers were interested in SSBs due to increase in popularity over the same time period in which age at menarche has decreased.

The main limitation of an analysis such as this is the potential for other health and lifestyle factors to be affecting age at menarche. In addition, The Growingup Today Study was not designed specifically to answer the current question, so may not have been able to measure all factors that might have been considered, if this was the main aim.

What did the research involve?

The Growingup Today Study included 9,033 girls, 5,227 of whom had data available for inclusion in this study.

A baseline questionnaire was given in 1996 when the girls were aged 9-14 years, with annual follow-up questionnaires up until 2001. In 1996, ‘97 and ’98, a 132-item questionnaire for young people and adolescents assessing what they ate and drank (a food frequency questionnaire) was given to the participants. They were asked how often they consumed a typical serving size of specified foods and drinks during the past year. For drinks, the serving size was one can/glass for soda and diet soda, one glass for non-carbonated fruit drinks (including Hawaiian Punch, lemonade, Koolaid and other non-carbonated fruit drinks), and one glass/can/bottle for sweetened iced tea. Total consumption of SSBs were calculated as the sum of these drinks. The total did not include diet soda or non-fizzy fruit juice, which were assessed separately.

Each follow-up questionnaire asked whether the girls had started their periods, and when.

The researchers calculated how the likelihood of menarche over time for girls in each category of SSB consumption compared with girls who drank the least SSBs (two or fewer servings per week). They adjusted for total energy intake and various other potential confounders, including physical activity, BMI, birthweight, ethnicity, mother’s age at menarche, family composition, and eating meals together as a family.

What were the basic results?

The average (median) age at menarche in this study was 13.1 years. Girls who drank more SSBs were more likely to have an earlier menarche.

After adjustment for all confounders, girls at any age between 9 and 18.5 years who had not yet started their periods were on average 22% more likely to start their periods in the following month if they drank the most SSBs (more than 1.5 SSB servings per day, equivalent to more than 10.5 servings per week) than girls who drank the least SSBs (2 or fewer SSB servings per week; hazard ratio (HR) 1.22, 95% confidence interval (CI) 1.11 to 1.35).

Girls who drank the most SSBs started their period at an average age of 12.8 years of age, which was 2.7 months earlier than girls who drank the least SSBs.

Looking at individual drinks, drinking the highest amounts of non-fizzy fruit drinks and sugar-sweetened fizzy drinks were associated with increased risk of starting menarche compared to the lowest consumption of these drinks. However, consumption of fruit juice or diet fizzy drinks did not affect age at menarche.

How did the researchers interpret the results?

The researchers conclude that, “more frequent SSB consumption was associated with earlier menarche in a population of US girls”. They acknowledge that though they adjusted for a variety of possible confounders, there is still the chance that factors other than SSB consumption are influencing the results. They also say that they did not measure SSB consumption during early childhood, which may also affect age at menarche.

Conclusion

People should not be overly concerned by this study’s findings, as they cannot prove that drinking SSBs directly causes earlier puberty in girls – they can only show a link.

Also, the difference between girls who drank the most SSBs in terms of when they started their period was an average of just 2.7 months earlier than girls who drank the least, which seems a relatively small difference.

There are various limitations to this study – not least the possibility that the results are being influenced by confounding, which the researchers acknowledge. Nutrition is already known to play a role in the timing of first periods, with higher BMI and calorie intake linked to earlier periods. Though they have tried to adjust for these and other factors that could be having an effect (including physical activity), there is still the possibility that their effect or those of other factors have not been removed. It is difficult to know how much of a direct and independent effect – if any – SSBs could be having.

Other points of limitation include that the possibility of inaccurate recall of SSB consumption and that the assessments may not be representative of longer-term consumption patterns. The first assessments were taken when the girls were around the age of 9-14 years – a time when many girls will be starting their periods anyway. This also makes it difficult to establish any cause and effect relationship. As the researchers say, SSB consumption during earlier childhood may be an important time period that they have not measured.

The study results are also for a US population who may differ from the UK, both in terms of their SSB consumption, and other factors that may influence age at menarche.

Even if SSB consumption does cause earlier menarche, it is difficult to know what health effects, if any, this would have. While it is true that earlier menarche is recognised as one possible risk factor for breast cancer, for example, this study did not assess any health outcomes other than menarche.

It is uncertain how much of an impact the small time difference in age of menarche seen in this study could have on breast cancer risk. The authors state that previous research has suggested that a one year decrease in the age at menarche is thought to increase breast cancer risk by around 5%. Therefore, they consider the 2.7 month reduction in age to be only “modest”. There are also a wide range of other health and lifestyle factors associated with breast cancer risk, some of which (alone or in combination) may have a greater influence than age at menarche.

Nevertheless, whatever the limitations of this study, SSBs are by their nature high in sugar and calories. High intake could contribute to an increase in risk of overweight and obesity if the calories are not burned off. Overweight and obesity are associated with many detrimental effects upon health, and sugar can also lead to tooth decay in later life.

There is normally a non-sugar alternative available to the most popular SSBs.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Links To The Headlines

Sugary drinks may cause menstruation to start earlier, study suggests. The Guardian, January 28 2015

Sugary drinks ‘can bring on a girl’s periods earlier’: Youngsters who drink more than one a day begin puberty at younger age. Daily Mail, January 28 2015

Fizzy drinks cause early puberty and increases cancer risk in girls, study finds. The Daily Telegraph, January 28 2015

Soft drinks may cause girls to start their periods early, scientists say. Metro, January 27 2015

One and a half cans of fizzy drink a day raises breast cancer risk. Daily Mirror, January 28 2015

Links To Science

Carwile JL, Willett WC, Spiegelman D, et al. Sugar-sweetened beverage consumption and age at menarche in a prospective study of US girls. Human Reproduction. Published online January 27 2015