Milk Products and Asthma

Introduction

Asthma is a chronic inflammation of the lining of the airways of the lungs and has several triggers which can vary with individuals.¹  Food allergies may trigger asthma or worsen asthma symptoms.¹  With regards to milk allergies, the incidence among infants is estimated to be about 2-3%, and tends to be outgrown before age 3 so that less than 0.5% of adults are estimated to be affected.² It is important for studies to take food allergies into account when assessing the role of certain foods in asthma development and control. Unfortunately, this isn’t always the case which may contribute to confounding of results.

The evidence

A double-blind randomized controlled trial explored whether dairy products induce bronchoconstriction in adults with asthma.³ Twenty adults were assigned to drink 300 ml of cow’s milk or 300 ml of rice beverage (placebo). There were no differences between the groups for standard respiratory measures such as forced expiratory volume and peak expiratory flow.

Another randomized controlled trial examined the effects of milk on bronchial airflow, measured by standard spirometry in 25 adults with mild asthma.⁴ Participants in this double-blind crossover study were randomly assigned to ingest a solution containing cow’s milk powder or a placebo solution. There were no important differences in pulmonary function results between the two groups.

A prospective cohort study of 61,909 pregnant women examined the relationship between dairy intake during pregnancy and the development of asthma in their offspring.⁵ The authors found a “suggestive protective association” for maternal consumption of whole milk and regular-fat yogurt and infant asthma while maternal intake of low-fat yogurt was suggestive of increased risk of child asthma.

Two prospective studies^6,7 explored maternal dietary intakes during pregnancy and/or lactation and asthma development in their children:

• Consumption of milk, butter and total milk products during pregnancy and lactation was not associated with increased risk of asthma;
• Margarine consumption during lactation was associated with an increased risk of asthma by 96%;
• Higher intake of saturated fat and palmitic acid was found to have a protective association with asthma (45% to 49% decreased risk, respectively);
• Lower arachidonic acid (n-6 polyunsaturated fat) intakes during pregnancy had a protective association with risk of asthma.

Another prospective study examined associations between maternal consumption of dairy products, calcium and vitamin D during pregnancy and wheeze in their children at 16 to 24 months.⁸ This study, including 763 mother-child pairs, suggests protective roles against wheeze, a common sign of asthma in children:

• Higher consumption of total dairy products, milk, cheese and calcium during pregnancy was associated with a decreased risk of wheeze in their children;
• Consumption of full-fat, but not low-fat, milk was related to a reduced risk of wheeze;
• Higher vitamin D intake during pregnancy was also associated with a reduced risk of childhood wheeze.

A study comprised of 723 children between 8 and 10 years, 246 of whom were diagnosed with asthma, found that infrequent milk consumption (< 2 times/week) doubled the risk of asthma in girls.⁹ While overweight status alone was associated with a 39% increased risk of asthma, the combination of infrequent milk consumption and overweight was associated with a 3.6-fold increase in the risk of asthma in girls.

A longitudinal study of 696 newborns that were part of the "Study on the Prevention of Allergy in Children in Europe" (SPACE) looked at milk consumption and asthma development up to age 3.¹⁰ Milk consumption was not associated with asthma development.

Data from 2,978 children participating in the PIAMA birth cohort study¹¹ revealed that daily consumption of regular-fat milk and butter were associated with a reduced risk of asthma compared to consumption of less than once a week. There was no association for reduced fat milk.

A review paper by Alwarith et al.¹² published in Nutrition Reviews examined the association of various dietary factors in the development and control of asthma in children and adults. However, a critical analysis reveals several important weaknesses and limitations with this review as it pertains to milk products and asthma.

Potential mechanisms

The components of milk products that could play a beneficial role in the etiology and control of asthma include fatty acids, calcium and vitamin D. 

Data from a large U.S. national study (NHANES III) showed that lower serum vitamin D levels are associated with an increased risk of upper respiratory tract infections; and, that the burden of respiratory infections associated with lower serum vitamin D levels appears to be even greater in those with chronic respiratory diseases such as asthma and COPD.¹³

Conclusions

Milk products are not associated with an increased risk of asthma or adverse effects on control of asthma unless a person is allergic to milk protein and develops asthma symptoms as a result.

Emerging scientific evidence indicates that the consumption of regular-fat milk products may reduce the risk of asthma, but further research is needed to provide more definitive answers, particularly regarding the role of specific milk products.

More studies are also needed to clarify how specific fatty acids, calcium and vitamin D may decrease the risk of asthma and/or improve asthma symptoms.