Sweetened Milk Drinks Now Linked to Type 2 Diabetes

April 30, 2015

A new study indicates, for the first time, a link between the consumption of sweetened milk drinks and type 2 diabetes, indicating that efforts to reduce intake of sugar-sweetened beverages (SSBs) should be extended to include milkshakes and flavored milk, say the researchers.

"Past research typically thought of SSBs as soft drinks such as fizzy drinks, colas, squashes, and juice drinks, but our study raises the possibility that the habitual daily consumption of sweetened milk drinks…is also related with a higher risk of new-onset diabetes," senior author Nita Forouhi, MRCP, PhD, from the University of Cambridge School of Clinical Medicine, United Kingdom, told Medscape Medical News.

As well as the association between type 2 diabetes and sweetened milk drinks, the study also calculated that, for each 5% increase of a person's total energy intake provided by sweet drinks, the risk of developing type 2 diabetes may increase by 18%.

And replacing the daily consumption of one serving of a sugary drink with either water or unsweetened tea or coffee can lower the risk of developing diabetes by between 14% and 25%, the scientists stress.

The new findings help "to provide tangible support for the dietary guidance (from the World Health Organization and other public-health agencies) to limit the percent contribution of free sugars to total energy intake and indicates that sugary beverages are important contributors," Dr Forouhi said.

"All healthcare and allied professional as well as public-health bodies can provide advice about reducing the consumption of free sugars in the diet. Limiting or eliminating the consumption of sugary beverages and replacing them with healthier alternatives, such as water and unsweetened tea or coffee, is one of the easiest ways to achieve that goal," she added.

First Study to Use Detailed 7-Day Food Diaries

The authors assessed the beverage consumption of 25,639 UK resident adults without diabetes at baseline (1993–1997) who were participating in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk study.

They used comprehensive 7-day food diaries, and this is the first study of its kind to employ this very detailed dietary assessment, said Dr Forouhi.

"The participants recorded everything that they ate and drank for 7 consecutive days covering weekdays and weekend days, with particular attention to type, amount, and frequency of consumption and whether sugar was added by the participants. This allowed us to examine, for instance, sweetened and unsweetened tea or coffee intake, which other studies could not do," she explained.

During 10.8 years of follow-up, 847 incident type 2 diabetes cases were verified.

After adjustment, there were positive associations, with a hazard ratio (HR) for type 2 diabetes per serving per day of 1.21 for soft drinks, 1.22 for sweetened-milk beverages, and 1.22 for artificially sweetened drinks, but there were null associations for sweetened tea and coffee (0.98) and for fruit juice (1.01).

More Research Needed on Role of Artificially Sweetened Drinks

After further adjustment for adiposity (using body mass index and waist circumference as markers of obesity), there remained a higher risk of diabetes associated with consumption of both soft drinks and sweetened milk drinks, but the link with artificially sweetened beverages (ASB) was attenuated (HR, 1.06).

"Our study showed that in simple analyses there was an increased risk of type 2 diabetes in those consuming ASBs, but that people who drank more of these tended to be overweight or obese, which is probably why they were consuming these drinks preferentially in the first place, as part of weight management, a classic case of so-called reverse causation," Dr Forouhi said.

Despite the fact they found no evidence of diabetes risk associated with ASBs, Dr Forouhi cautioned that some other studies have shown a positive association between consumption of artificially sweetened drinks and risk of diabetes even after accounting for obesity.

"At present, based on other good research, we can say that ASB consumption in place of sugary options can play a part in weight management, but for its role in diabetes prevention more research is needed to tease out the complex interrelationships between ASB consumption, obesity, weight change, and diabetes," she explained.

First to Distinguish Between Sweetened and Unsweetened Tea, Coffee

The current findings on SSBs are "in keeping with other publications, with an increased risk of type 2 diabetes per serving of soft drinks, independent of adiposity," the researchers say.

Some of the findings related to the consumption of tea and coffee are novel, however.

Although there is accumulated evidence to suggest that both tea and coffee are inversely associated with incident diabetes, "to our knowledge, this is the first epidemiological study to distinguish between sweetened and unsweetened tea or coffee," they observe.

"In the current study, unsweetened tea or coffee was inversely associated with incident diabetes, but sweetened tea or coffee overall had a null association."

"Our findings show that drinking unsweetened tea or coffee was associated with lower risk of type 2 diabetes and that replacing sweetened tea or coffee consumption with unsweetened tea or coffee was also related with lower risk of developing type 2 diabetes," Dr Forouhi told Medscape Medical News.

Asked whether drinking sweetened tea or coffee would be better than consuming sweetened soft drinks or sweetened milk drinks, she said the study did not specifically examine this, "as our question was focused on replacing a sugary drink with a nonsugary drink."

This also means that it is difficult to give advice with regard to fruit-juice consumption, she noted. The null association between fruit juice and incidence of diabetes seen "is in keeping with some previous work, but there are also mixed findings elsewhere."

"Our null finding does not give a license to freely consume fruit juice habitually and frequently….Be mindful that juice does contribute to the total free-sugars intake, which adds up over the course of days, weeks, and months.

"Further research is still needed to clarify whether juice is or is not okay to consume on a habitual regular basis in the context of diabetes," she observed.

And the findings "make an evidence-based case for drinking unsweetened tea or coffee in preference [to sweetened versions]," she stressed.

Association Between Sweetened Milk and T2D "Unsurprising"

The other novel finding of a positive association between consumption of sweetened-milk beverages and type 2 diabetes is perhaps no great shock, the researchers say. "As added sugar contributes about half of the total sugar content of beverages such as milkshakes and flavored milks, this association is unsurprising."

Nevertheless, this finding is of concern "because flavored milk is now recognized as a major contributor to added sugar intake."

And while Dr Forouhi says these results "should be replicated in other studies, it certainly sounds a note of caution that the past focus solely on nonmilk sweetened drinks may miss out an important class of sweetened beverages that could be related with adverse health effects through the nonmilk free sugars."

She told Medscape Medical News that the research did not specifically examine whether plain milk was a good substitute for sweetened milk beverages or other SSBs. "We cannot directly address the issue currently, but this will be for future research to pursue."

In conclusion, she says the new study findings "provide practical information to consumers that replacing the habitual consumption of a sugary drink with plain water or unsweetened tea or coffee can play a part in reducing the risk of future type 2 diabetes, so giving some helpful alternatives."

This work was supported by program grants from the Medical Research Council UK and Cancer Research UK. The authors have reported no relevant financial relationships.

Diabetologia. Published online April 30, 2015. Available at http://www.diabetologia-journal.org.

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