Dairy consumption and lung cancer risk: a meta-analysis of prospective cohort studies

Cow's Milk in Human Nutrition and the Emergence of Plant-Based Milk Alternatives

Cow's milk is considered a complete food, providing high-quality protein and essential micronutrients, including vitamins and minerals. For medical reasons or as a lifestyle choice, consumers are replacing cow's milk with plant-based milk alternatives (PBMA); some perceive them as healthier alternatives to cow's milk due to their low saturated fatty acid content and no cholesterol content. However, the nutritional composition of PBMA is quite variable between different types and even within, which makes a comparison with cow's milk a complex issue. Furthermore, the consumption of PBMA has been associated with the development of some diseases in infants and children. Meanwhile, the consumption of cow's milk in human health is a controversial issue since it has been associated with a favorable effect in some diseases (such as obesity, type 2 diabetes, and Alzheimer's) and a negative effect in others (such as prostate cancer risk and Parkinson's disease); while in some diseases, there is no consensus in the cow's milk consumption effect. The aim of this review is to make a nutritional comparison of cow's milk with PBMA and to clarify the potential health issues related to their consumption.

Dairy product consumption and development of cancer: an overview of reviews

OBJECTIVES

To provide a comprehensive systematic overview of current evidence from pooled analyses/meta-analyses and systematic reviews (PMASRs) pertaining to dairy consumption and incident cancer and/or all-cause or cancer-specific mortality.

DESIGN

Overview of reviews.

SETTING

Community setting.

PARTICIPANTS

The unit of analysis is PMASRs. A total of 42 PMASRs was included in this overview of reviews.

INTERVENTIONS/EXPOSURES

Any dairy product consumption (eg, milk, yogurt, etc).

PRIMARY AND SECONDARY OUTCOMES MEASURES

Primary outcome measure is development of any type of cancer. Secondary outcome measures are all-cause mortality and cancer-specific mortality.

RESULTS

From 9693 citations identified, we included 42 PMASRs (52 study reports) published between 1991 and 2017. Thirty-one (74%) of these was pooled analyses/meta analyses, and only 11 (26%) were systematic reviews and meta-analyses. There was a wide variability in the type of study designs included within the other PMASRs, thus contributing to variable and, in instances, divergent estimates of cancer risk for several cancer subtypes. For example, only one systematic review and meta-analysis exclusively included prospective study designs. Most PMASRs were of low to moderate quality based on the Assessing the Methodological Quality of Systematic Reviews (AMSTAR) scores. The median AMSTAR score was 5 (IQR 2-7). Our overview identified conflicting evidence from PMASRs on association between dairy consumption and incident cancers or mortality. Heterogeneity in summary estimates reflected the inclusion of variable study designs and overall low methodological quality of individual PMASRs.

CONCLUSIONS

The association between dairy consumption and cancer risk has been explored in PMASRs with a variety of study designs and of low to moderate quality. To fully characterise valid associations between dairy consumption and risk of cancer and/or mortality rigorously conducted, PMASRs including only high-quality prospective study designs are required.

TRIAL REGISTRATION NUMBER

CRD42017078463.

Milk and dairy products: good or bad for human health? An assessment of the totality of scientific evidence

Background

There is scepticism about health effects of dairy products in the public, which is reflected in an increasing intake of plant-based drinks, for example, from soy, rice, almond, or oat.

Objective

This review aimed to assess the scientific evidence mainly from meta-analyses of observational studies and randomised controlled trials, on dairy intake and risk of obesity, type 2 diabetes, cardiovascular disease, osteoporosis, cancer, and all-cause mortality.

Results

The most recent evidence suggested that intake of milk and dairy products was associated with reduced risk of childhood obesity. In adults, intake of dairy products was shown to improve body composition and facilitate weight loss during energy restriction. In addition, intake of milk and dairy products was associated with a neutral or reduced risk of type 2 diabetes and a reduced risk of cardiovascular disease, particularly stroke. Furthermore, the evidence suggested a beneficial effect of milk and dairy intake on bone mineral density but no association with risk of bone fracture. Among cancers, milk and dairy intake was inversely associated with colorectal cancer, bladder cancer, gastric cancer, and breast cancer, and not associated with risk of pancreatic cancer, ovarian cancer, or lung cancer, while the evidence for prostate cancer risk was inconsistent. Finally, consumption of milk and dairy products was not associated with all-cause mortality. Calcium-fortified plant-based drinks have been included as an alternative to dairy products in the nutrition recommendations in several countries. However, nutritionally, cow's milk and plant-based drinks are completely different foods, and an evidence-based conclusion on the health value of the plant-based drinks requires more studies in humans.

Conclusion

The totality of available scientific evidence supports that intake of milk and dairy products contribute to meet nutrient recommendations, and may protect against the most prevalent chronic diseases, whereas very few adverse effects have been reported.