Search

Excess mortality in a population is one of the hallmarks of an influenza epidemic. Apart from the pandemic years, 1918-1919, 1957 and 1968-1969, annual excess mortality has occurred 16 times in Sweden during the period 1911-1988. An unusually high mortality was caused by Influenza A Sichuan 2/87 (H3N2), the unexpected appearance of which at the beginning of November 1988 started an intensive epidemic in Sweden, while other European countries had a relatively mild influenza season. Swedish deaths in December totalled 10,500-2,200 more than expected; age groups over 65 years accounted for 95 per cent of the mortality, and those over 80 (N = 350,000 in Sweden) for 1,400 deaths. 0.4 percent of those over 80 died. The excess mortality is to be explained by the high proportion of the elderly in the Swedish population and the very low rate of influenza vaccination before the outbreak. As the increase in the proportion of the very elderly can be expected to continue, future influenza epidemics will result in even higher mortality unless adequate prophylactic measures are taken.

The contents of total nitrogen, nonprotein nitrogen, lactose, and individual milk proteins have been determined in human milk from well-nourished Swedish mothers. Breast milk samples from 50 mothers at different stages of lactation (up to 170 days) were collected. Furthermore, three mothers gave samples repeatedly throughout the whole lactation period. The protein content in mature milk was found to be 0.8 to 0.9% by amino acid analysis. The nitrogen content and the contents of the major human milk whey proteins, alpha-lactalbumin and lactoferrin, are very high for the first few days, then decrease rapidly and reach, thereafter, the more slowly declining level of mature milk. Nonprotein nitrogen and the nonspecific milk protein serum albumin are present in constant concentrations throughout lactation. The daily milk volumes were determined and found to be 500 to 600 ml in the very early part and 700 to 800 ml in the later part of the lactation period.

The contents of iron, copper, zinc, calcium and magnesium were determined in human milk samples from 18 Ethiopian and 23 Swedish women. The Ethiopian women belonged to two groups with different socio-economic situations, a non-privileged and a privileged group. Both groups had an excessively high dietary iron intake--20 to 30 times that of the Swedish women--from the iron-rich traditional diet. In spite of this, the mean concentrations of iron in the milk, as well as of zinc and magnesium, were similar in all three groups. The mean copper concentration, however, was significantly lower in the Ethiopian than in the Swedish milk samples, the lowest mean value occurring in the privileged group. In contrast, a significantly higher mean calcium concentration was found in milk samples from the Ethiopian women than from the Swedish, the highest mean concentration being noted in the non-privileged group. The levels of minerals in breast milk showed no correlation to the birth weight of the infants or the length of gestation. Our data suggest that an excessively high dietary iron intake does not increase the breast milk content of iron in mothers with a good iron status. The reasons for the differences in the content of copper between the Ethiopian and Swedish milk samples are unclear. The higher calcium content in milk from the Ethiopian mothers, despite a low dietary calcium intake may be a result of an increased endogenous cholecalciferol synthesis due to greater exposure to sunshine.

The true protein content of human milk is 0.9%, in well-nourished as well as malnourished mothers. Casein constitutes only about 20% of the protein nitrogen in human milk. The remaining 80% is derived from the whey proteins, the three dominant components being alpha-lactalbumin, lactoferrin and secretory IgA. alpha-lactalbumin is a subunit of lactose synthetase. Lactoferrin is an iron-binding glycoprotein which plays a role in the defence against gastro-intestinal infections and is probably also involved in iron transport in the gut. Secretory IgA is comparatively stable at low pH; it is resistant to proteolytic enzymes and plays an essential role in the immunological defence against gastro-intestinal infections. Lysozyme is a minor component of the whey proteins and represents an active enzyme with a bactericidal effect. The nutritional and immunological significance of the marked differences with respect to the nitrogen and protein compositions of human milk and cow's milk should not be underestimated, but need further elucidation.

Breast milk from underprivileged and privileged Ethiopian mothers was collected at different stages of lactation and analyzed for total nitrogen, nonprotein nitrogen, lactose, and individual milk proteins (lactoferrin, alpha-lactalbumin, serum albumin, IgG and IgM). These values and the milk volume of one meal were compared to corresponding results from well-nourished Swedish mothers. No significant differences between the levels of these constituents or the milk volumes were found between the two groups of Ethiopian mothers. When comparison was made between breast milk from these two Ethiopian groups and the Swedish group, the former two showed significantly higher values for the iron-binding protein lactoferrin.