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Children grow up hearing that milk and other dairy foods can help them develop strong and healthy bones. But could dairy also be good for kids’ brains—and their mental health? Researchers have been working to answer this question, which has taken on greater urgency given the rise in youth struggling with mental health [1]. According to the World Health Organization, about 14% of 10- to 19-year-olds globally have a mental health condition, with anxiety and depression being most common.

In general, a healthier dietary pattern has been associated with a reduced risk of depression [2], but studies attempting to tease out the specific effects of dairy products have found mixed results. A recent systematic review of 13 studies in adults reported that most found either no association or results that varied based on type of dairy product, gender, or population group [3]. Similarly, several studies in youth have found no relationship between dairy consumption and mental health, but recent reports from Iran and Korea found a positive association between dairy consumption and mental health in adolescents [4,5].

Seeking to investigate this relationship among youth in China, researchers Zhiyong Zou and Yanhui Dong from the Institute of Child and Adolescent Health at Peking University, along with their colleagues, recruited students enrolled in Beijing schools to participate in a cross-sectional study [6]. The study included 1,353 youth between the ages of 7 and 17 years old. Students were asked to complete questionnaires about their physical activity, diet, and symptoms of depression and anxiety. Their parents also provided background information, including parental education level, household income, single child status, and whether parents were smokers.

The study, which was published in the Journal of Affective Disorders in December 2022, found that about 54% of participating youth consumed dairy products habitually, on six or more days per week. Another 35% had dairy products on two to five days per week, and 11% had dairy on just one day per week or not at all.

When the researchers looked at the study participants’ mental health, they found that the habitual dairy consumers had lower rates of depression and anxiety than those who consumed less dairy. For example, among those who consumed dairy on six or more days per week, about 12% had symptoms of depression, and 26% had symptoms of social anxiety. In comparison, 21% of those who had dairy just once per week or not at all had symptoms of depression, and 40% had symptoms of anxiety.

The children and adolescents in the study who consumed more dairy products also appeared to be more advantaged and have healthier lifestyles in other ways. On average, they ate more fruits and vegetables, were younger and more physically active, and their parents were better educated. However, when the researchers accounted for these differences, they found that dairy consumption was still associated with lower odds of depression and anxiety, though the relationship was somewhat attenuated.

The results were surprising and were strengthened by the large number of children and the wide age range included in the study, wrote Jieyu Liu, a doctoral student at Peking University and the first author of the study, in an email interview with SPLASH! Milk Science Update. However, the study also had several limitations. For example, the data were self-reported by students in brief questionnaires, and more objective and detailed measures of diet and physical activity, and clinical assessments by mental health professionals could have yielded more accurate results.

In addition, the observational design of this study means that its findings can only identify correlations—in this case, between dairy consumption and a lower prevalence of symptoms of depression and anxiety—and it cannot provide direct evidence that dairy consumption prevents depression or anxiety. There could be alternative explanations for this correlation, Liu acknowledged, and the study did not measure several important and known risk factors for adolescent depression, such as family history of depression, exposure to bullying, growing up in a negative family environment, experiencing trauma, or substance use [7]. Without a better accounting of the factors contributing to youth mental health, it’s difficult to draw conclusions about how dairy intake may affect risk of depression or anxiety.

That said, there are several possible mechanisms for how dairy foods might support better mental health. For example, they are good sources of several nutrients known to play roles in brain health: calcium regulates neurotransmitter release; milk proteins are rich in the amino acid tryptophan, a precursor to serotonin; and vitamin D may protect against inflammation and oxidative stress. The type of dairy product may also matter. A recent study in Finnish adults found that only high-fat dairy consumption, and not low-fat or total dairy intake, was associated with a lower risk of depressive symptoms [8]. And a meta-analysis published earlier this year concluded that eating fermented dairy products like yogurt and cheese was associated with a significant decrease in the risk of depression, perhaps mediated by live microbes in these foods and their effect on the gut-brain axis [9].

Future research on this question should include more detailed data on the types and amounts of dairy products consumed, as well as other nutritional factors, such as intake of red meat, snack foods, and fast foods, Lui wrote in the email interview. Well-designed prospective studies and intervention trials are also needed to better understand the complex relationships between diet and mental health.

References

1. Young people’s mental health is finally getting the attention it needs. Nature. 2021 Oct 598(7880):235-236.
2. Selvaraj R, Selvamani TY, Zahra A, Malla J, Dhanoa RK, Venugopal S, Shoukrie SI, Hamouda RK, Hamid P. Association between dietary habits and depression: A systematic review. Cureus. 2022 Dec 14(12):e32359.
3. Hockey M, McGuinness AJ, Marx W, Rocks T, Jacka FN, Ruusunen A. Is dairy consumption associated with depressive symptoms or disorders in adults? A systematic review of observational studies. Critical Reviews in Food Science and Nutrition. 2020;60(21):3653-3668.
4. Khayyatzadeh SS, Shafiee M, Far PE, Ziaee SS, Bagherniya M, Ebrahimi S, Boromand N, Ferns GA, Ghayour-Mobarhan M. Adherence to a healthy dietary pattern is associated with less severe depressive symptoms among adolescent girls. Psychiatry Research. 2019 Feb 272:467-473.
5. Park S, Rim SJ, Lee JH. Associations between dietary behaviours and perceived physical and mental health status among Korean adolescents. Nutrition & Dietetics. 2018 Jul 75(5):488-493.
6. Liu J, Chen M, Ma Y, Ma T, Gao D, Li Y, Wang X, Chen L, Ma Q, Zhang Y, Ma J, Zou Z, Dong Y. Habitual dairy consumption is inversely associated with depressive and social anxiety symptoms among children and adolescents aged 7-17 years: Findings from a cross-sectional study in Beijing, China. Journal of Affective Disorders. 2022 Dec 319:309-317.
7. Wahid SS, Ottman K, Hudhud R, et al. Identifying risk factors and detection strategies for adolescent depression in diverse global settings: A Delphi consensus study. Journal of Affective Disorders. 2021 Jan 279:66-74.
8. Hockey M, Mohebbi M, Tolmunen T, Hantunen S, Tuomainen T, Macpherson H, Jacka FN, Virtanen JK, Rocks T, Russunen A. Associations between total dairy, high-fat dairy and low-fat dairy intake, and depressive symptoms: findings from a population-based cross-sectional study. European Journal of Nutrition. 2023 Feb 62(1):227-237.
9. Luo Y, Li Z, Gu L, Zhang K. Fermented dairy foods consumption and depressive symptoms: A meta-analysis of cohort studies. PLoS ONE. 2023 Feb 18(2):e0281346.

“The views and opinions expressed in this publication are those of the contributing authors and editors and do not necessarily represent the views of their employers or IMGC sponsors.”

Scientists know little about the flavor of human milk, but they do know that flavor plays a large role in breastfeeding [1]. In a new study, researchers have constructed the first-ever flavor wheel for human milk—a tool that can be used to objectively describe and quantify the substance’s flavor and sensory properties [2].

“Flavor is an important factor influencing infants’ food choices,” said Yajun Xu, Vice Dean of the School of Public Health at Peking University in China and one of the study’s lead authors, in an email to SPLASH! The results, he added, provide “a solid and essential understructure for flavor research … [and] will enable us to further decode the substantial flavor substances not only in human milk but also in infant formula.”

Xu and his colleagues obtained a milk sample from 18 mothers—six from each of three provinces in eastern China: Beijing, Jiangsu and Anhui. They then assembled a panel of 12 sensory evaluators with experience evaluating dairy products to assess the milk samples in a laboratory at Beijing Technology and Business University.

To build the flavor wheel, panelists first generated a list of 84 descriptors of human milk from six randomly selected samples. The researchers then worked with panelists to standardize the terms by applying a widely-accepted method called “international organization standardization of sensory descriptors selection.” They settled on 53 terms: 30 descriptors of aroma, 14 descriptors of flavor, and nine descriptors of mouthfeel. These terms were organized into 18 groupings, each of which were subsets of three main sensory modalities—aroma, flavor, and mouthfeel.

Next, the researchers paired down the list of descriptors from the flavor wheel by assessing which ones the panelists found to be most intensely present in the samples they had initially screened. After removing some descriptors and combining others, they ended on 15 terms that described the flavor variability in their samples. These terms were fishy, dairy-fat, metallic/iron, cooked, flour, dairy-sweet, and grassy/green for aroma; sweet, umami, creamy, fishy, and boiled milk for taste; and silky, fattiness, and mouthfulness, which the researchers defined as “the feel of coating, long-lasting, thickness,” in the paper as for mouthfeel.

Finally, the team asked panelists to analyze the full set of 18 collected samples based on the 15 descriptors. The most prominent sensory attributes that the panelists identified were dairy-fat and dairy-sweet for aroma, sweet and creamy for flavor, and silky for mouthfeel. But the samples tended to have highly different scores for each descriptor. To explore relationships within those differences, the researchers grouped the samples in multiple ways, such as by region, by lactation time, and by fat content. “Surprisingly, the samples with a similar fat content exhibited more analogous sensory profiles,” Xu said in an email. This suggests that fat content is a key determinant of flavor for human milk, he said.

The researchers note that in their study, the tasters were adults, and not infants—and it’s unknown whether adults and infants experience flavor the same way. Nonetheless, the work makes it possible to home in on the specific flavor molecules responsible for taste differences, the researchers say. Another key goal is to reduce or eliminate flavor differences between human milk and infant formula, which have been identified in earlier work. Producing formula that more closely mimics human milk’s flavor may prove helpful for infants who struggle with breastfeeding.

References

1. Raimbault C, Saliba E, Porter RH. The Effect of the Odour of Mother’s Milk on Breastfeeding Behaviour of Premature Neonates. Acta Paediatr. 2007, 96, 368–371.
2. Yu M, Zheng C, Xie O , Tang Y, Wang Y, Wang B, Song H, Zhou Y, Xu Y, Yang R. Flavor Wheel Construction and Sensory Profile Description of Human Milk. Nutrients. Dec 19;14(24):5387.

“The views and opinions expressed in this publication are those of the contributing authors and editors and do not necessarily represent the views of their employers or IMGC sponsors.”

If your New Year’s resolution for 2023 was to eat healthier, you’re not alone. Fifty percent of Americans surveyed at the end of 2022 planned to use the change in calendar year to make improvements to their diet [1]. With so much dietary advice available at the click of a mouse, it can be difficult to discern diet fads from scientifically informed guidance. The Dietary Guidelines for Americans (DGA) [2] were designed to help us separate the wheat from the chaff when it comes to healthy eating choices across the life span. But despite being based on “the most current body of nutritional science” [2], the recent edition of the DGA falls short of their promise when providing guidance on dairy foods.

To combat cardiovascular disease (CVD)—the leading cause of death for Americans—the current DGA recommends avoiding full-fat dairy foods in favor of low- or non-fat versions [2]. This guidance incorrectly implies that all dietary sources of saturated fat have a negative effect on heart health [3]. Instead, different saturated fat-containing foods can have different health effects [3, 4]. Previous research has shown dairy-derived saturated fats have neutral or even positive effects on body fat, cholesterol, heart disease, and numerous biomarkers associated with cardiovascular health [3].

More evidence that full-fat dairy can be part of your 2023 healthy eating plan comes from a new study [4] investigating the relationship between dairy fats and dyslipidemia, a condition of high cholesterol and high levels of triglycerides (“fat”) in the blood. The study participants (n = 2,391) were a subset of the Framingham Offspring cohort, a group of adults that have provided dietary and heart health data since the early 1970s. For each participant, specific amounts of dairy-derived saturated fats and non-dairy saturated fats were calculated from two sets of 3-day diet records provided between four and seven years apart [4]. Then, roughly four years and eight years after the second set of dietary data were collected, each participant’s weight and height were recorded and each provided a fasting blood sample that was analyzed for two markers of inflammation (C-reactive protein, fibronectin); cholesterol, including low-density lipoprotein (LDL), high-density lipoprotein (HDL), and very-low-density lipoprotein (VLDL); particle sizes for all types of cholesterol; and triglycerides (TG) [4].

This may seem like data overkill, but there is good reason for measuring so many factors. Cardiovascular health cannot be assessed by just checking cholesterol; LDL and HDL levels are also important. For example, someone with high LDL but also high HDL has a reduced CVD risk compared with someone with high LDL and low HDL. And then within the low- and high-density dichotomy, particle size matters as well. Saturated fats that increase small LDL particle size pose a larger risk to CVD than do those that increase larger LDL molecules [3, 5, 6]. Finally, inflammation is also a risk factor for CVD—it is possible for dietary fats to have a neutral effect on blood lipids while positively or negatively influencing the production of markers of inflammation [3].

Participants with the highest intakes of dairy-derived saturated fat had blood profiles associated with low risk for dyslipidemia and inflammation [4]. Interestingly, the specific associations depended on participant sex. Male participants with higher mean intakes of dairy-derived saturated fats had a lower CVD risk profile: lower levels of inflammation markers, higher HDL cholesterol, lower VLDL concentrations, larger LDL and HDL particle size, and lower TG concentration [4]. Among females, higher mean intakes of saturated fat from dairy foods were associated with lower levels of body fat, but there was no significant association with inflammation biomarkers. In both males and females, higher intakes of saturated fat from dairy were associated with a lower TG:HDL ratio [4].

The Framingham Offspring Study was prospective in design, meaning it can demonstrate an association between dairy-derived saturated fat and lower CVD risk but cannot prove that saturated fat from dairy foods is the cause for lower cholesterol, lower TG, or less inflammation. However, the length of the study period, representing nearly 16,000 days of food intake, and the specific focus on separating saturated fat intake from other dietary sources of saturated fat strengthen the validity of the identified associations. It was not immediately clear to the study team why they observed sex differences in the strength of their associations. Future studies will help determine if saturated fats have different physiological effects in males compared with females or if there was a confounding factor that the Framingham study failed to account for.

For those that grew up with the dogma that all saturated fats were artery cloggers, the cardiovascular benefits of full-fat dairy may be hard to swallow. The stigma of saturation is strong—but if dark chocolate can become a health food, so can whole milk! Saturated fats from dairy foods are unique because they contain more short- and medium-chain fatty acids than do fats from other animal sources. These fatty acids have different metabolic effects, potentially raising HDL cholesterol more effectively than fatty acids with longer chains of carbons [5]. And unlike a hamburger, dairy-derived saturated fats are delivered with minerals and bioactive peptides that have positive health effects such as lowering blood pressure and reducing inflammation. The most successful New Year’s resolutions are ones that don’t require an entire overhaul of people’s lifestyles. The same is true for nutritional advice. Rather than revise the guidelines to encourage full-fat dairy intake, a more successful solution could be to remove guidance about fat content; simply encourage Americans to meet their daily dairy intake without specifying the type of fat [7]. Food-based rather than fat-based nutritional guidance will hopefully become a dietary fad that sticks.

References

1. https://www.statista.com/chart/29019/most-common-new-years-resolutions-us/
2. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2020-2025 Dietary Guidelines for Americans. 9th Edition. December 2020. Available at https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf
3. Sendra E. Dairy fat and cardiovascular health. Foods. 2020 Jun 26;9(6):838.
4. Yuan M, Singer MR, Pickering RT, Moore LL. Saturated fat from dairy sources is associated with lower cardiometabolic risk in the Framingham Offspring Study. The American Journal of Clinical Nutrition. 2022 Dec; 116(6):1682-92.
5. de Oliveira Otto MC, Mozaffarian D, Kromhout D, Bertoni AG, Sibley CT, Jacobs DR Jr, Nettleton JA. Dietary intake of saturated fat by food source and incident cardiovascular disease: the Multi-Ethnic Study of Atherosclerosis. The American Journal of Clinical Nutrition. 2012; 96(2):397-404.
6. Mozaffarian D. Saturated fatty acids and type 2 diabetes: more evidence to re-invent dietary guidelines. The Lancet Diabetes and Endocrinology. 2014; 2(10):770-772.
7. McGovern C, Rifas-Shiman SL, Switkowski KM, Woo Baidal JA, Lightdale JR, Hivert MF, Oken E, Aris IM. Association of cow’s milk intake in early childhood with adiposity and cardiometabolic risk in early adolescence. The American Journal of Clinical Nutrition. 2022 Aug; 116(2):561-71.

“The views and opinions expressed in this publication are those of the contributing authors and editors and do not necessarily represent the views of their employers or IMGC sponsors.”

Asthma, which affects 14% of children and their families around the world [1], is the most common chronic disease of childhood. Several studies have linked an early exposure to antibiotics to an increased risk of asthma [2].

In 2020, a microbiologist from the University of British Columbia, Charisse Petersen, and her colleagues reported that decreasing the use of antibiotics was correlated with lower rates of asthma, and the effect was likely because of a healthier gut microbial community [3]. Although reducing antibiotic use is important, it’s not an option for all children. “We can’t eliminate antibiotics,” Petersen said in an interview. “Some babies really need these medications.”

An effort to understand how to help these children led the researchers to investigate the links between breastfeeding and asthma. Thus far, the evidence has been murky: some studies suggested breastfeeding had a protective effect and reduced the risk of asthma, whereas others found no benefit. The confusion stems, in part, from the immense variability in the composition of breastmilk, antibiotic dosing, and other environmental exposures that can trigger asthma.

In a new study, the team turned to data from the CHILD cohort study, a project that observes the health of children from mid-pregnancy until adolescence [4]. For the current work [5], Petersen and her colleagues included 2,521 children from the larger cohort, 2,102 of whom received no antibiotics in the first year of life, 286 received systemic antibiotics while breastfeeding, and 133 received antibiotics but were not breastfed. The team found that compared with children who received no antibiotics, those who received the medicines without breastfeeding were three times more at risk of developing asthma by age five. “But if kids were being breastfed by when they received those antibiotics, this risk almost went away,” Petersen said. “We found that breastfeeding itself might be one of the most beneficial things if a child needs antibiotics in the first year of life.”

But the researchers did not just stop there. Knowing that not all children can be breastfed and there can be significant variations in the chemistry of milk that could contribute to the positive effect of breastfeeding on asthma development, Petersen and colleagues continued on to characterize why breastmilk appeared to be protective.

The team sequenced the gut microbiome of 1,338 children from samples collected in early infancy (~3 months) and at about 1 year of age to characterize microbial changes. Compared with children who received no antibiotics, those who received them but did not breastfeed had significantly lower diversity of their gut bacteria. But this decrease was absent in those who were also breastfed when receiving the medicines. Since the developing gut microbiome is sensitive to nutrients, drugs and other external forces, antibiotics can cause significant perturbations, Peterson explained. “Breastfeeding seemed to counteract some of the imbalance that the antibiotic was causing,” she added.

To confirm whether the positive effect of breastfeeding on asthma development was a result of the components of milk or because of maternal milk’s effects on gut microbes, the team compared the genetic diversity of bacterial strains across the samples. They found that breastfeeding was linked to an increase in the abundance of a species named Bifidobacterium longum. Comparing three subspecies, they narrowed the benefits down to one subspecies, B. longum infantis. The authors write in their paper that “B. infantis may act as a keystone species to buffer the effects of antibiotics on the functional infant.”

The subspecies B.infantis thrives on human milk, so the authors examined whether specific components of milk could boost levels of this bacteria. “It was very important for us to find a way to afford this same protection for kids who can’t be breastfed but still need antibiotics,” Peterson said.

The investigators found that some of the breastmilk fatty acids, such as linoleic acid and arachidonic acid, were negatively correlated with the abundance of the subspecies B. infantis in the infant gut. But many human milk oligosaccharides (HMOs) correlated with higher levels of B. infantis, suggesting that “these HMOs may increase B. infantis colonization and maintain functional diversity in the microbiome in children receiving antibiotics,” the authors wrote in the study. Although more research is needed, these data could eventually inform ways in which HMOs and B. infantis can be used together to reduce the risk of asthma in children who need antibiotics. “A hope of our study is to inform research that is moving in that direction, Peterson said.

References

1. Pearce N, Aït-Khaled N, Beasley R, Mallol J, Keil U, Mitchell E, Robertson C. Worldwide trends in the prevalence of asthma symptoms: phase III of the International Study of Asthma and Allergies in Childhood (ISAAC). Thorax. 2007 Sep 1;62(9):758-66.
2. Ni J, Friedman H, Boyd BC, McGurn A, Babinski P, Markossian T, Dugas LR. Early antibiotic exposure and development of asthma and allergic rhinitis in childhood. BMC Pediatrics. 2019 Dec;19(1):1-8.
3. Patrick DM, Sbihi H, Dai DL, Al Mamun A, Rasali D, Rose C, Marra F, Boutin RC, Petersen C, Stiemsma LT, Winsor GL. Decreasing antibiotic use, the gut microbiota, and asthma incidence in children: evidence from population-based and prospective cohort studies. The Lancet Respiratory Medicine. 2020 Nov 1;8(11):1094-105.
4. Subbarao P, Anand SS, Becker AB, Befus AD, Brauer M, Brook JR, Denburg JA, HayGlass KT, Kobor MS, Kollmann TR, Kozyrskyj AL. The Canadian Healthy Infant Longitudinal Development (CHILD) Study: examining developmental origins of allergy and asthma. Thorax. 2015 Oct 1;70(10):998-1000.
5. Dai DL, Petersen C, Hoskinson C, Del Bel KL, Becker AB, Moraes TJ, Mandhane PJ, Finlay BB, Simons E, Kozyrskyj AL, Patrick DM. Breastfeeding enrichment of B. longum subsp. infantis mitigates the effect of antibiotics on the microbiota and childhood asthma risk. Clinical Advances. 2023 4(2): 92-112.

“The views and opinions expressed in this publication are those of the contributing authors and editors and do not necessarily represent the views of their employers or IMGC sponsors.”