Milk drinking and possible protection of the respiratory epithelium

Vitamins and respiratory disease: antioxidant micronutrients in pulmonary health and disease

The lungs are continually exposed to relatively-high O(2) tensions, and as such, in comparison with other organs, they represent a unique tissue for the damaging effects of oxidant attack. At particular times during a lifetime this every day challenge may increase exponentially. The first oxidative insult occurs at birth, when cells are exposed to a sudden 5-fold increase in O(2) concentration. Thereafter, the human lung, from infancy through to old age, can be subjected to deleterious oxidative events as a consequence of inhaling environmental pollutants or irritants, succumbing to several pulmonary diseases (including infant and adult respiratory distress syndromes, asthma, chronic obstructive pulmonary disease, cystic fibrosis and cancer) and receiving treatment for these diseases. The present paper will review the concept that consumption of a healthy diet and the consequent ability to establish and then maintain adequate micronutrient antioxidant concentrations in the lung throughout life, and following various oxidative insults, could prevent or reduce the incidence of oxidant-mediated respiratory diseases. Furthermore, the rationale, practicalities and complexities of boosting the antioxidant pool of the respiratory-tract lining fluid in diseases in which oxidative stress is actively involved, by direct application to the lung v. dietary modification, in order to achieve a therapeutic effect will be discussed.

Milk consumption does not lead to mucus production or occurrence of asthma

There is a belief among some members of the public that the consumption of milk and dairy products increases the production of mucus in the respiratory system. Therefore, some who believe in this effect renounce drinking milk. According to Australian studies, subjects perceived some parameters of mucus production to change after consumption of milk and soy-based beverages, but these effects were not specific to cows' milk because the soy-based milk drink with similar sensory characteristics produced the same changes. In individuals inoculated with the common cold virus, milk intake was not associated with increased nasal secretions, symptoms of cough, nose symptoms or congestion. Nevertheless, individuals who believe in the mucus and milk theory report more respiratory symptoms after drinking milk. In some types of alternative medicine, people with bronchial asthma, a chronic inflammatory disease of the lower respiratory tract, are advised not to eat so-called mucus-forming foods, especially all kinds of dairy products. According to different investigations the consumption of milk does not seem to exacerbate the symptoms of asthma and a relationship between milk consumption and the occurrence of asthma cannot be established. However, there are a few cases documented in which people with a cow's milk allergy presented with asthma-like symptoms.

Dietary antioxidants and environmental stress

Air is one of our most important natural resources; however, it is also in the front line for receiving environmental pollution. Air quality decreased markedly following the industrial revolution, but it was not until the great London Smog in 1952 that air quality made it onto the political agenda. The introduction of the Clean Air Act in 1956 led to dramatic decreases in black smoke and SO2 concentrations over the next two decades, as domestic and industrial coal-burning activities ceased. However, as these improvements progressed, a new threat to public health was being released into the air in ever-increasing quantities. Rapid motorisation of society from the 1960s onwards has led to the increased release of atmospheric pollutants such as tiny particles (particulate matter of <10 microm in aerodynamic diameter) and oxides of N, and the generation of the secondary pollutant O3. These primary and secondary traffic-related pollutants have all proved to be major risks factors to public health. Recently, oxidative stress has been identified as a unifying feature underlying the toxic actions of these pollutants. Fortunately, the surface of the lung is covered with a thin layer of fluid containing a range of antioxidants that appear to provide the first line of defence against oxidant pollutants. As diet is the only source of antioxidant micronutrients, a plausible link now exists between the sensitivity to air pollution and the quality of the food eaten. However, many questions remain unanswered in relation to inter-individual sensitivity to ambient air pollution, and extent to which this sensitivity is modified by airway antioxidant defences.

Asthma and allergic diseases in schoolchildren: third cross-sectional survey in the same primary school in Ankara, Turkey

We investigated prevalence and determinants of asthma and allergic diseases in a cross-sectional survey of schoolchildren aged 6-14 in 2002. This was the third of a series of cross-sectional surveys, conducted in 1992 and 1997, in the same school in Ankara, Turkey. Questionnaire including information on house characteristics, dietary habits, past and current exposures and diseases were distributed to 1064 children (523 boys, 541 girls) and filled by the parents at home. Percentage of children having a pet was significantly higher (1992: 7.9, 1997: 22.9, 2002: 21), but that of passive smoking was significantly lower (1992: 74, 1997: 64, 2002: 64.1) in 1997 and 2002 when compared with 1992. Current prevalence percentage of asthma (1992: 8.3, 1997: 9.8, 2002: 6.4), wheeze (1992: 11.9, 1997: 13.3, 2002: 6.4), hay fever (1992: 15.4, 1997: 14.1, 2002: 7.2), and eczema (1992: 4, 1997: 4.3, 2002: 1.8) were significantly lower in 2002 compared with 1992. Multiple logistic regression analysis model for current wheeze included ingestion of cow's milk (no regular ingestion: reference, ORs and 95% CIs, <1 glass/day: 0.5, 0.3-1.0; at least 1 glass/day: 0.3, 0.2-0.7), ingestion of red meat (2.2, 1.2-3.8), and currently holding a dog (6.1, 1.6-23.4). Multiple logistic regression analysis model for current hay fever included ingestion of red meat (1.8, 1.1-2.9) and father's education (none of the parents finished secondary school: reference, secondary school to university: 0.5, 0.2-1.0). Our findings suggested that current prevalence of asthma and allergic diseases decreased among schoolchildren in Ankara, in the last 10 yr, and ingestion of milk and red meat could have a role in the occurrence of asthma and hay fever. Detailed assessment of dietary habits is required to test this hypothesis.

Vitamin A, cigarette smoking, and airway obstruction

The hypothesis that vitamin A, or foods rich in vitamin A such as milk, protects against the development of airway obstruction was tested in a subsample of data from the 1971-1975 National Health and Nutrition Examination Survey. The relative risk (estimated by relative odds) of having airway obstruction, defined as a FEV1/FVC less than or equal to 65%, was measured for different levels of nutrient and food group intakes after adjustment for age, sex, Quetelet Index, caloric intake, and cigarette smoking. Among the white respondents (never smokers or current smokers) whose recalled diet could be considered as typical of their usual diet, the relative odds of having airway obstruction was inversely related to vitamin A intake (x2 for trend = 7.2, p less than 0.01). In the analysis by food groups, the adjusted relative odds of airway obstruction for meat and poultry were 2.4 (95% confidence limits: 1.0 to 5.8) and for milk 1.6 (95% confidence limits: 1.0 to 2.5). The association of airway obstruction with lack of vitamin A or milk intake was clearer among smokers. These findings suggest that a diet poor in vitamin A increases the risk of airway obstruction, and are consistent with the previously reported association of chronic bronchitis, milk intake, and smoking.