Is There a Milk-Mucus Connection?

For nearly a millennium, clinicians, consumers, coaches, and competitors contended that the consumption of dairy products contributes to a variety of respiratory difficulties. A cursory assessment of current beliefs among physicians, athletes, and those with asthma, indicates that more than 50% uphold the position that milk consumption makes mucus despite the lack of direct evidence (Thiara and Goldman, 2012; Lee and Dozor, 2004; Woods et al., 1996; Arney and Pinnock, 1993).

Feasibility of an adverse response following a milk challenge and physiological responses upon milk exclusion require clinical assessments. Among those with chronic diseases that affect the airway, such as chronic bronchitis, asthma, and COPD, hypersecretion of mucus by airway goblet cells may
reflect increased activity of two mucin-producing genes, MUC5AC in surface epithelial cells and MUC5B in submucosal glands (Jackson, 2001).

Among healthy individuals, there is a decreased distribution and size of these goblet cells as one moves distally to the periphery of the bronchial tree. However, among those with chronic respiratory disease, the size and number of submucosal glands is larger, which results in mucus hypersecretion. Thus peripheral airway passages become clogged with gel-forming mucin that continues to exacerbate the disease.

One hypothesis is that one genetic polymorphism of A2 bovine casein, known as A1, may alter intestinal permeability, and that another bovine peptide, ß-casomorphin-7, stimulates mucin secretion via upregulation of MUC5AC gene, particularly in those presenting asthma (Kost et al., 2009). While increased mucus production is characteristic of many respiratory diseases, direct evidence of the potential milk-mucus connection has not been established (Alawa et al., 1996). Importantly, European Food Safety Authority and Food Standards Australia New Zealand indicate that milk with these and related peptides is safe and does not contribute to immunological or noncommunicable disorders.

Over the past two decades, many survey assessments and clinical studies investigated the milk-mucus relationship among individuals with asthma. Several questionnaires indicate approximately 30% of the population believes in this relationship, whereas nearly 40% refrain from consuming liquid milk products (Pinnock et al., 1989; Pinnock et al., 1990). Consistent with the milk-mucus effect, approximately 80% of believers perceive a variety of throat sensations, such as thickness, cough, coating, and stickiness following milk consumption (Arney and Pinnock, 1993). When a non-milk beverage was used as a placebo for comparative purposes, the classic milk-mucus descriptors for symptoms were similar in both groups and not specific to milk (Pinnock and Arney, 1993). A more recent report indicated that up to 70% of parents of children with asthma, allergies, or cystic fibrosis contend that milk increases mucus and thus strive to limit milk consumption when they are not well (Lee and Dozor, 2004).

Nearly 80% of those who self-diagnose a food and asthma association restrict or eliminate the alleged dietary culprit, whereas less than 3% respond to a placebo-controlled challenge (Woods et al., 1996). A recent review of the clinical evidence among those with asthma indicates milk consumption, with few
exceptions, is unlikely to aggravate respiratory difficulties or significantly alter pulmonary functions. These data also indicate that a direct link in the proposed milk-mucus relationship cannot be established.

Importantly, the elimination or dietary restriction of milk products may contribute to unintended consequences, such as nutrient insufficiencies and growth faltering among children (Wüthrich et al., 2005; Thiara and Goldman, 2012).

Despite the practice of avoiding dairy products among many athletes who believe in the milk-mucus theory, there have not been any clinical studies to validate this position. On the contrary, there is a plethora of evidence that supports the importance of dairy products for their contribution to muscle protein synthesis, muscle protein accretion, and improved post-exercise recovery (Phillips et al., 2009; Spaccarotella and Andzel, 2011; Pritchett and Pritchett, 2012; James, 2012).

Consumers, coaches, competitors, and clinicians have perpetuated misinformation for centuries, including anecdotal testimony regarding the milk-mucus theory. It is incumbent upon all of us to examine and apply the medical and scientific evidence, which in this case indicates regular consumption of milk products does not contribute to hypersecretion of mucus and subsequent respiratory difficulties among most individuals, even among those at risk.

References included in this article are available from the authors.

Heather Rodriguez, R.D.,
Contributing Editor
Clinical Dietitian, Peterson Regional
Medical Center, Kerrville, Texas
[email protected]

Roger Clemens, Dr.P.H.,
Contributing Editor
Chief Scientific Officer,
Horn Company, La Mirada, Calif.
[email protected]