| Code assigned and year of study | Site of study | Explanation | [Ref.] |
| Inherent difference | |||
| 1922 | USA | “These findings suggest a possible racial factor…Poverty, environment and social status, with the ensuing advantages and disadvantages, do not seem to influence the lung capacity of children.” | [8] |
| 1968 | Trinidad | “Results ‘underline’ the relative importance of inherited racial characteristics rather than acquired physical attributes.” | [9] |
| 1978 | USA | “The agreement between the two studies suggests that the lower FVC and FEV1 values among blacks are related to genetic rather than to environmental variables.” | [10] |
| 1999 | USA | “There are known to be differences in normal lung volumes among various ethnic or racial groups. For example, lung volumes (FVC and FEV1) are about 12% lower in black subjects compared with white subjects. Similarly, normal values for several Asian populations have been shown to be lower than those for white subjects…Various explanations, such as body habitus, have been proposed for these differences, but race or ethnicity itself seems to be the determinant factor.” | [11] |
| Anthropometric difference | |||
| 1962 | Taiwan | “Perhaps the daily habitual posture, especially the sitting habit, of Chinese makes the position of the diaphragm lower, which in turn affects the lung volume. Further studies may be indicated for proper explanation of this theory.” | [12] |
| 1976 | USA | “It seems unlikely that differences in socioeconomic status would explain such consistent observations from all locations. It is also unlikely that socioeconomic factors affecting growth influenced the data because there were no significant differences in height or weight between the black and white children…In part, the racial differences in lung size may be explained by the smaller ratio of sitting height to standing height in blacks compared to whites.” | [13] |
| 2004 | USA | “The reasons for these racial differences are not well defined. Differences in thoracic height and body stature have been shown to affect spirometric volumes. Orientals have been shown to have smaller lung volumes and larger sitting-to-total-height ratios than whites of the same age and height.” | [14] |
| Environmental and social factors | |||
| 1969 | India | “Milledge et al…attributed the smaller lung volumes in Indians to climatic conditions.” | [15] |
| 1984 | South Africa | “When subject to scrutiny, the available evidence does not support a clear thesis of racial or ethnic differences in spirometric lung functions. Moreover, fixed percentage discounting from White normal values for Blacks cannot be substantiated. Studies purporting to find ethnic determinants of FVC have generally not controlled for social confounding factors known to be strongly associated with nutritional status, respiratory morbidity and occupational exposures. Predicted values within the same ethnic group vary as widely as predicted values between groups. This variability of FVC values in the different Black populations studied implies that factors other than race are operative.” | [16] |
| 2001 | India | “This paper presents evidence to suggest that a well-defined component of ‘racial’ or ‘ethnic’ variation between Caucasian and Asian children may be unrelated to race per se, and could be potentially regulatable by therapeutic (dietary supplementation) or socioeconomic interventions, lending support to the hypothesis that other areas of comparative physiological disadvantage in populations should not be ascribed to racial differences, without the exclusion of poverty or health care-related, potentially treatable, aetiological mechanisms.” | [17] |
| Technical factors | |||
| 1988 | USA | “With the sample sizes typically available for developing prediction equations, sampling variation will remain an explanation for all but extreme differences.” | [18] |
| Other | |||
| 1993 | Israel | “Anthropometric measurements could not explain interethnic variability in spirometric values;…could be due to ethnic differences in growth velocity.” | [19] |
| Mixed explanations | |||
| 1927 | China | “It may prove that there is a larger variability in nationals of one country, caused by climate, activity and bodily build than is found between nations or races.” | [20] |
| 1978 | South Africa | "The reasons for ethnic differences in ventilatory function are not clear, but could relate to differences in lung elastic recoil, or to the smaller sitting-to-standing height ratio in Blacks compared with Caucasians. The differences in FEV1 and FVC between Coloureds and Caucasians in this study are considered to be ethnic, despite the difference in physical characteristics between the two groups, since covariance analysis takes such physical characteristics into account....there is no evidence to suggest that malnutrition disproportionately reduces lung growth.” | [21] |
| 2001 | USA | “Sitting height accounted for 35–39% of the race difference in both sexes. Poverty index accounted for about 7.5% and 2.5% of the racial difference in women and men, respectively, whereas the effect of education accounted for about 2% in women and 4.7% in men. With further adjustment for BMI, we could account for only about half of the racial difference in FEV1 and FVC. We conclude that the racial difference in lung function is only partially explained by a shorter upper body segment in African-Americans. Although low socioeconomic indicators are related to lower lung function, they explain only a small proportion of this racial difference…The main finding of this analysis is that we can explain only about half of the racial difference in FEV1 and FVC between white individuals and African-Americans by accounting for sitting height, BMI, and socioeconomic indices such as poverty index or education.” | [22] |
FVC: forced vital capacity; FEV1: forced expiratory volume in 1 s; BMI: body mass index.