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Eating more dark chocolate was associated with a lower risk of type 2 diabetes, an analysis of prospective cohort studies suggested.

Among participants across three studies of healthcare workers, those who consumed ≥5 servings per week of dark chocolate had a 21% lower risk of type 2 diabetes compared with those who never or rarely consumed dark chocolate (P=0.006 for trend), reported Qi Sun, MD, ScD, of the Harvard T.H. Chan School of Public Health in Boston, and colleagues in .

There was no significant association between consumption of milk chocolate and type 2 diabetes, but intake of milk chocolate was positively associated with weight gain, while this was not the case for dark chocolate.

"We were surprised to see a stark contrast between dark and milk chocolate," co-author Binkai Liu, MS, also of Harvard T.H. Chan School of Public Health, told 番茄社区app. "While dark chocolate was associated with a lower risk of type 2 diabetes, milk chocolate showed no such benefit and was even associated with weight gain. This difference underscores the importance of chocolate type and its nutrient composition."

"Advising patients to enjoy dark chocolate occasionally as part of a balanced and nutrient-rich diet could be a way to integrate these insights into practical recommendations," she added.

Chocolate is high in polyphenols, including flavanols (part of the larger flavonoid group), and have shown an association between higher dietary flavonoid consumption and decreased type 2 diabetes risk.

Though flavonoids may confer antioxidant, anti-inflammatory, and vasodilatory benefits, the relationship between chocolate consumption and diabetes remains "controversial," the authors wrote, due to observational studies with inconsistent findings, and a lack of inquiry into health effects by chocolate subtype.

"We made efforts to adjust for various dietary, lifestyle, and socioeconomic variables, but residual confounding remains a possibility," Liu said.

Simin Liu, MD, ScD, of the University of California Irvine, who was not involved in the study, told 番茄社区app that "the new findings, while promising, should be interpreted with caution. Observational studies like this can show associations but cannot definitively prove cause and effect."

"It's plausible that the flavanols in dark chocolate may contribute to improved insulin sensitivity and glucose metabolism, which could offer some protection against type 2 diabetes," he noted. "However, it's important to consider other lifestyle factors that may be influencing the results."

For this analysis, Sun and team used data from the Nurses' Health Study (NHS) and the Nurses' Health Study II (NHSII) (both all female), as well as the Health Professionals Follow-up Study (HPFS; all male). Total chocolate consumption baselines for the NHS and HPFS were in 1986, and in 1991 for the NHSII, when comprehensive food frequency questionnaires were first implemented. The second baseline, for chocolate subtype analyses, were in 2006 for the NHS and HPFS and 2007 for the NHSII, when the survey added questions about chocolate types.

Participants' diets were assessed every 4 years, with questions about average consumption of a standard portion size of chocolate in the past year, with nine frequency levels ("never, or less than once per month" to "≥6 per day"). Starting in later years, participants were asked, "How often do you consume milk chocolate (bar or pack)?" and "How often do you consume dark chocolate?"

Other variables assessed included race/ethnicity, body weight, waist circumference, smoking status, alcohol consumption, multivitamin use, menopausal status and postmenopausal hormone use, oral contraceptive use, hypertension, hypercholesterolemia, and family history of diabetes. Physical activity and body mass index were measured over time. Diabetes was self-reported in biennial questionnaires and confirmed by study doctors with a supplementary questionnaire, which collected more details about diagnoses and treatment.

In total, 192,208 participants were included from the three trials in the total chocolate intake analysis, with 111,654 included in the analysis on chocolate types. The mean ages at first baseline were 52.3, 36.1, and 53.1 for the NHS, NHSII, and HPFS, respectively. For baseline 2, they were 70.4, 52.3, and 68.3, respectively. Most participants were non-Hispanic white.

In the analysis on total chocolate intake, participants who consumed ≥5 servings per week of any chocolate had a 10% lower relative risk of type 2 diabetes compared with those who never or rarely consumed chocolate, but this was not a significant trend (P=0.07).

Participants with higher chocolate intake had higher energy, saturated fat, and added sugar intakes. Higher levels of dark chocolate consumption were associated with higher-quality diet, as assessed by the Alternate Healthy Eating Index-2010 (based on food frequency questionnaire responses), and greater consumption of fruit and vegetables, epicatechin, and total flavonoids. The opposite was true for milk chocolate consumption.

The authors were limited by potential confounding, and a limited number of people with type 2 diabetes in the higher chocolate consumption groups. Most of the participants in the chocolate subtype analyses were white adults over 50 at baseline, which could limit the generalizability of the findings to other populations.

Moreover, chocolate consumption in the overall study population was low compared with the national average, which was another limitation.

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