Physical activity patterns and anthropometric changes in Senegalese women observed over a complete seasonal cycle

Season of birth and subsequent body size: the potential role of prenatal vitamin D

OBJECTIVES

The relationship between season of birth and various physical and psychological outcomes was reported in many studies, although the underlying mechanism still remains unrecognized. The aim of this study was to explore the season-of-birth effect on body size in the sample of 1,148 eight-year-old Polish urban children and propose the mechanism responsible for this effect.

METHODS

The children were examined three times at their birthdays and at two cross-sectional surveys. Effects of the season of birth were checked by fitting the cosine function to empirical values and by comparison between two groups born in different periods of the year.

RESULTS

Data gathered at three examinations led to the same results: season-of-birth effect occurred only in boys and only in those relatively shortly breastfed and/or descended from the families of low-socioeconomic status. Specifically, the individuals born in October-April were taller (by 2-3 cm), heavier (by 2-3 kg), and fatter than those born in May-September.

CONCLUSIONS

The following explanatory mechanism has been formulated: insolation in Poland is minimal in November-February (winter period), and so ultraviolet absorption and vitamin D production is then the lowest. Vitamin D regulates embryo's cellular differentiation, and its deficiency triggers permanent developmental changes. Therefore, individuals conceived in autumn (i) are at the greatest risk of early vitamin D deficiency, (ii) are born in summer, and (iii) are relatively small in their further lives. The contribution of low-socioeconomic status, short breastfeeding, and being a male to the occurrence of the season-of-birth effect is also discussed.

Relationships between anthropometry, cardiorespiratory fitness indices and physical activity levels in different age and sex groups in rural Senegal (West Africa)

BACKGROUND

A high level of activity is commonplace in traditional subsistence societies. Physiological characteristics of individuals, including body composition and physical fitness, could be limiting factors when performing daily tasks.

OBJECTIVES

The study investigated the relationships between cardiorespiratory fitness, nutritional status and physical activity patterns, so as to test the hypothesis that these relationships are less straightforward in children than in adults.

STUDY DESIGN

Four different groups of individuals from rural Senegal were investigated: 99 10-13-year-old children of both sexes (11.1 +/- 1.5 years old) from two settings in Senegal (Lambaye and Podor), 43 adolescent girls (15.5 +/- 0.5 years), and 30 adult women (17-40 years).

METHODS

Subjects undertook a step test, and anthropometric measurements were collected. Continuous heart rate (HR) monitoring was performed for 8-12 h. The flex-HR method was used to estimate levels of activity (per cent of time spent under or over the flex-HR).

RESULTS

Ten to 13-year-old children and adolescent girls presented slight degrees of malnutrition. Adult women were apparently not nutritionally deprived. Differences in cardiorespiratory fitness were found among 10-13-year-old children, while adult women performed better than adolescent girls. Children from Lambaye had a higher level of activity than children from Podor. Similarly, adult women were more active than adolescent girls. No relationships were found between cardiorespiratory or anthropometric measurements and per cent of time spent above the flex-HR (> flex-HR) in 10-13-year-old children. In contrast, in adult women and adolescent girls, body composition and cardiorespiratory indices were significant predictors of activity levels.

CONCLUSION

Our data support the hypothesis that activity levels are less dependent upon physiological characteristics in children than in adults in traditional subsistence societies.

Energetic factors and seasonal changes in ovarian function in women from rural Poland

Female mammals can optimize their fitness by temporal suppression of reproductive function in response to unfavorable environmental conditions. Since reproduction is energetically demanding for a human female, ovarian function is expected to be sensitive to factors influencing energy availability and metabolism. Dieting and exercise in women from industrial countries, and low-calorie diet and workload in women from developing countries, are often associated with ovarian suppression. This study shows that in Polish rural women seasonal changes in workload correlate with seasonal changes in indices of ovarian function (progesterone measured in saliva samples collected daily for six menstrual cycles for each subject). Mean levels of energy expenditure of the most work demanding weeks of the summer exceeded mean levels of energy expenditure during winter by 37%. Energy intake in this population was sufficient throughout the year. During the summer, when physical work was most intense, low values of progesterone levels were observed (178.2 pmol/L in July and 182.2 pmol/L in August), indicating ovarian suppression. Mean progesterone levels rose to 234.6 pmol/L in October when levels of energy expenditure were lower due to cessation of harvest-related activities. As indicated by several causal models tested through path analysis, energy expenditure was the only variable responsible for suppressed progesterone levels during the summer. Variables describing the nutritional status and energy balance did not correlate significantly with progesterone levels; neither body weight nor body fat or seasonal changes of these variables seem to influence ovarian function in this population. Thus work-related energy expenditure does not need to lead to negative energy balance in order to cause suppression of reproductive function in women.