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PubMed1988

Seasonal and hormonal control of pulsatile LH secretion in the dairy goat (Capra hircus).

In Exp. 1, the changes in pulsatile LH secretion at the onset of the breeding season were observed in 20 intact, mature Saanen does. Blood was sampled every 20 min for 6 h each week from the beginning of August until the onset of ovulatory activity, as evidenced by cycles in plasma progesterone. The first doe ovulated at the end of August and all were cycling by the end of September. As the first ovulation approached, LH pulse frequency increased by 67% and mean levels of LH increased by 47%. These changes were progressive rather than abrupt. In Exp. 2, seasonal changes in the inhibition of pulsatile LH secretion by ovarian steroids were studied in ovariectomized Saanen does. The animals were untreated (N = 4) or given subcutaneous oestradiol implants (N = 4) and blood was sampled every 10 min for 6 h, twice during the breeding season and twice during the anoestrous season. In each season, the second series of samples was taken after the animals had been treated with progesterone, administered by intravaginal implants. Season did not significantly affect LH secretion in goats not treated with oestradiol, but LH pulse frequency was 54% lower during the anoestrous season than during the breeding season in oestradiol-treated goats. Mean LH concentrations were affected in the same manner as pulse frequency, but pulse amplitude was increased by oestradiol treatment in both seasons. Progesterone had no detectable effect on LH secretion in either season. In Exp. 3, the response to repeated melatonin injections at a set time after dawn was investigated in 11 oestradiol-treated, ovariectomized goats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Seasonal variation in pituitary-gonadal function in free-ranging impala (Aepyceros melampus).

Blood, testicular biopsies and electroejaculates were collected from adult male impala, free-ranging in the Kruger National Park (Republic of South Africa), during the breeding (rut; April-May) and nonbreeding (September-October) seasons. Blood samples were collected at 5-min intervals for 120 min from anaesthetized males (n = 7 impala/group) treated intravenously with saline, gonadotrophin-releasing hormone (GnRH: 1 microgram/kg body weight) or human chorionic gonadotrophin (hCG: 10 or 30 iu/kg). Semen was collected from six more animals during the breeding season and 12 animals during the nonbreeding season using a standardized electroejaculation protocol. Ejaculates obtained during the nonbreeding season were of inferior quality to those collected during the breeding season, and were characterized by lower sperm concentrations, poorer sperm motility and more morphologically abnormal sperm forms. Within season, there were no differences in testosterone secretion between the two hCG doses, and these responses were similar to those observed after GnRH, but during the rut, testosterone secretion stimulated by both GnRH and hCG was approximately nine times greater than during the nonbreeding season. This seasonal increase in testosterone production was associated with a doubling in testicular volume and concentrations of luteinizing hormone (LH) receptors. Although concentrations of testicular follicle-stimulating hormone (FSH) receptors were similar between seasons, receptor content increased during rut as a result of increased testicular volume. In contrast to testosterone secretion, basal LH and FSH secretions were unaffected by season and GnRH-induced gonadotrophin secretion was reduced during rut.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Seasonal variation in perceived indoor environment and nonspecific symptoms in a temperate climate.

Few epidemiological studies have examined the effects of season on symptoms typical of sick building syndrome (SBS). The present study aims to clarify seasonal variation in a perceived indoor environment and SBS symptoms in a temperate climate. A total of 116 workers were recruited from office buildings in southern Japan that presented no apparent serious indoor problems. A validated questionnaire was distributed four times, once at the end of each season. Seasonal effects on the perceived indoor environment and SBS symptoms were investigated with a parametric test for repeated measurement of categorical data. Logits were used as the response function, and were compared to overall logits to determine the relevant odds ratios (OR). The effect of season/building interaction was also evaluated. Significant seasonal variation in the perceived indoor environment was found for temperature, dryness, air stuffiness, and static electricity (p for season, <0.05), although the seasonal patterns for temperature and dryness differed according to the building (p for interaction, <0.05). Symptoms in the mucous membrane (eyes, nose, and throat) and skin increased considerably in the winter and spring (p for season, <0.05), whereas general symptoms varied little, but such seasonality of symptoms was not modified by the building factor. The associations between perception of indoor environments and mucous and skin symptoms became stronger during winter and spring. The present results suggest that perceived indoor environments, nonspecific symptoms and their associations are closely associated with the season among office workers in a temperate climate.

Air Pollution, Indoor↗
PubMed2006

Soil characteristics of a hyperseasonal cerrado compared to a seasonal cerrado and a floodplain grassland: implications for plant community structure.

Savannas may be divided according to their seasonality into semi-seasonal, seasonal, hyperseasonal, or marshy savannas. Hyperseasonal savannas are characterized by the alternation of two contrasting stresses during each annual cycle, one induced by drought and fire and the other, by waterlogging. In South America, the largest savanna region is the Brazilian cerrado, in which there are few hyperseasonal areas that become waterlogged in the rainy season. The cerrado soils are generally well drained, but in central Brazil there is a small cerrado area in which the soil is poorly drained and which becomes waterlogged in the middle of the rainy season, allowing the appearance of a hyperseasonal cerrado. As long as soil is important in the ecology of the cerrado vegetation, we asked whether the waterlogging in this hyperseasonal cerrado implied that there were differences in soil characteristics in relation to a seasonal cerrado, which is not waterlogged in the rainy season, and to a floodplain grassland, which remains waterlogged throughout the year. In each environment, we randomly selected ten points, in which we collected soil samples in the mid-rainy season for chemical and granulometric analyses. For all variables, we found significant differences among the three environments, at least at one of the depths. Nevertheless, when we took into account all the variables together, we observed that the soils under the hyperseasonal and seasonal cerrados were similar and both were different to the soil under the floodplain grassland. The soil under the floodplain grassland was related to larger amounts of clay, silt, organic matter, phosphorus, aluminium, aluminium saturation, cation exchange capacity, and sum of bases, whereas soils under hyperseasonal and seasonal cerrados were related to higher pH values, base saturation, calcium, magnesium, and sand. As long as the soil under both cerrados was chemically and physically similar, the duration of waterlogging in the hyperseasonal cerrado is not long enough to alter its soil characteristics. Limitations to the plants growing on the hyperseasonal cerrado soil must be a consequence of the direct effects of flooding. Since cerrado plant species are dryland ones, the hypoxia caused by waterlogging may limit the number of cerrado species able to withstand these conditions.

Brazil↗
PubMed1989

Conception rate at first insemination in beef cattle: effects of season, age and previous reproductive performance.

The effects of season, age at previous parturition, and whether the female was retained because she failed to conceive or be detected in estrus during the previous breeding season were analyzed for first-service conception rate in beef cattle. Twelve years of reproductive data on females that were at least 50% Simmental were obtained from a single farm. All females detected in estrus were artificially inseminated during 42-d breeding seasons (52 d for heifers), starting either in June or November. The data, consisting of 9,071 first-service records, were described by a logit model and parameters were estimated using weighted least squares procedures. Age and previous reproductive performance (whether the female had failed to conceive or be detected in estrus during the previous breeding season) significantly affected first-service conception rate, as did the interaction between the two factors. Season of insemination, when considered across all other effects, did not influence first-service conception rate, but the interaction of season and previous reproductive performance was significant, as was the three-way interaction between season, age and previous reproductive performance. Except for those calving at 2.5 yr of age, females that were inseminated in the winter subsequent to parturition in the fall had the highest first-service conception rates. Those that did not conceive during the breeding season subsequent to parturition and were carried over to the following season had lower first-service conception rates, with the lowest being for females carried over to the winter breeding season.

Age Factors↗
PubMed2003

Seasonal variation in hospitalisation for hypertension-related morbidities in Sokoto, north-western Nigeria.

OBJECTIVE: To determine the relationship between hospital admissions of hypertension-related morbidities, seasons and meteorological factors in a tropical climate. STUDY DESIGN: Retrospective analysis of hospitalised patients (440) with hypertension-related morbidities including heart failure (36.4 %), stroke (34.8%), chronic renal failure (7.1%) and others (21.7%) from 1995 to 2000. The relationship between hospital admission, seasons and meteorological factors was determined using simple proportions, univariate, multivariate and regression analysis. RESULTS: The subjects were aged 21-85 years and represented 9.3 % of all hypertensives and 7.0% of medical admissions. Mean blood pressure was 187.3 +/- 34.0/120 +/- 23 mmHg. Mild, moderate and severe hypertension occurred in 30 (6.8%), 59 (13.4%) and 351 (79.8%) patients, respectively. The monthly admission rate ranged from 3-11; (mean 6.1 +/- 1.9) patients. Admission rates peaked in January/February and August/September, corresponding with the peaks of harmattan and the wet seasons, respectively. Mean monthly admission rates were significantly higher during harmattan than during the hot season (6.7 +/- 2 versus 5.2 +/- 1.4 patients; p < 0.05), and during wet season than during the hot season (6.4 +/- 1.9 versus 5.2 +/- 1.4 patients; p < 0.05). Considering the hypertensives as a whole, a significantly higher proportion of patients was hospitalised during the cold season than during the hot season (11% versus 8.2%; odds ratio = 1.34). Linear regression analysis showed that hospital admission was significantly associated with the monthly minimum temperature (p = 0.02) and solar radiation (p = 0.01). Multiple regression analysis revealed that hospital admission was also significantly associated with combined meterological factors (temperature, radiation, dust haze days and relative humidity) (p = 0.04). CONCLUSIONS: Hospital admissions of patients with hypertension-related morbidities showed seasonal variation. Appropriate clothing and health planning during cold seasons are recommended.

Adult↗
PubMed2002

Seasonal malaria attack rates in infants and young children in northern Ghana.

The incidence density of infection and disease caused by Plasmodium falciparum in children aged six to 24 months living in the holoendemic Sahel of northern Ghana was measured during the wet and dry seasons of 1996 and 1997. At the beginning of each season, a cohort composed of 259 and 277 randomly selected children received supervised curative therapy with quinine and Fansidar and primaquine for those with normal glucose-6-phosphate dehydrogenase activity. The 20 weeks of post-therapy follow-up consisted of three home visits weekly and examination of Giemsa-stained blood films once every two weeks. Blood films were also taken from children brought to clinic with illness. The incidence density of parasitemia after radical cure was 4.7 infections/person-year during the dry season and 7.1 during the wet season (relative risk = 1.51, 95% confidence interval [CI] = 1.25-1.81; P = 0.00001). Although the mean parasitemia count at time of reinfection in the dry season (3,310/microl) roughly equaled that in the wet season (3,056/microl; P = 0.737), the risk ratio for parasitemia > 20,000/microl during the wet season was 1.71 (95% CI = 1.2-2.4; P = 0.0025). The risk ratio for parasitemia > 20,000/microl with fever during the wet season was 2.45 (95% CI = 1.5-4.1; P = 0.0002). The risk ratio for anemia (hemoglobin < 8 g/dl) at first post-radical cure parasitemia showed no difference between seasons (1.0; 95% CI = 0.73-1.4; P = 0.9915). We did not see seasonal differences in anemia known to exist in this region, probably because the longitudinal cohort design using first parasitemia as an end point prevented the subjects from developing the repeated or chronic infections required for anemia induction. These findings bear upon the design of malaria drug and vaccine trials in holoendemic areas.

Anemia↗
PubMedDate not supplied

Sublingual immunotherapy and influence on urinary leukotrienes in seasonal pediatric allergy.

Sublingual immunotherapy has been suggested for the treatment of respiratory allergies. Many controversial studies have been reported on the efficacy of sublingual immunotherapy. The aim of this prospective study was to evaluate whether sublingual immunotherapy was effective according to clinical and laboratory results in pediatric allergies. Thirty-nine allergic, grass pollen sensitive children were admitted into the study. Sublingual immunotherapy was given over a 12-month period to 21 children (mean age 10.5 +/- 3.3 years), 10 of whom had seasonal allergic rhinitis and 11 seasonal allergic asthma. During the same period, 18 children (mean age 11.1 +/- 2.5 years), 10 with seasonal allergic rhinitis and eight with seasonal allergic asthma, received placebo. Symptom scores and drug requirements were recorded and urine samples were collected to detect urinary levels of leukotrienes (Uc-LTB4 and Uc-LTE4). In patients who received sublingual immunotherapy, the symptom scores of seasonal allergic rhinitis significantly decreased, but no statistically significant changes were observed in terms of symptoms of seasonal allergic asthma. Uc-LTE4 and Uc-LTB4 levels of seasonal allergic rhinitis, with a geometric mean and 95% confidence interval (CI), were significantly decreased from 216 (103-464) and 61 (22-198) pmol/mmol creatinine to 78 (29-159) and 35 (12-118) pmol/mmol creatinine, respectively (p < 0.05 and p < 0.05). On the other hand, Uc-LTE4 and Uc-LTB4 levels for seasonal allergic asthma were 180 (92-355) and 78 (44-258) pmol/mmol creatinine and decreased to 156 (72-402) and 69 (32-254) pmol/mmol creatinine, respectively. These changes were not statistically significant (p > 0.05). According to our clinical results and urinary levels of leukotrienes, which are mediators showing the severity of allergic inflammation, it can be suggested that sublingual immunotherapy may be useful in the treatment of seasonal allergic rhinitis but not of seasonal allergic asthma.

Administration, Sublingual↗
PubMed2003

Seasonal variation in meningococcal disease in Denmark: relation to age and meningococcal phenotype.

Seasonal variation has been shown in meningococcal disease (MD), but it is not known whether seasonal variation depends on age, gender and meningococcal phenotype. Based on complete registration of MD in North Jutland County, Denmark, during 1980-1999 (n = 413 cases), a Poisson regression model of a sinusoidal form was used to examine: (i) whether the seasonal variation in MD follows a sinusoidal pattern; (ii) the magnitude of seasonal variation in MD; and (iii) whether seasonal variation is related to age and gender and meningococcal phenotype. The peak-to-trough ratio (PTR) was used as a measure of the magnitude of seasonal variation. An overall seasonal variation in MD was found [PTR 2.0, 95% confidence interval (95% CI) 1.5-2.6]. There were differences between age groups and between phenotypes, but not between genders. The highest PTRs were observed for the age groups 5-9 y (PTR 4.9, 95% CI 2.1-11.9) and 10-14 y (PTR 3.7, 95% CI 1.4-9.7). No seasonal variation was found for children < 1 y (PTR 1.4, 95% CI 0.6-3.2) or teenagers 15-19 y (PTR 1.6, 95% CI 0.8-3.0). Among phenotypes the highest PTR was observed for C:2a:P1.2,5 (PTR 3.8, 95% CI 1.3-11.2). Thus, seasonal variation depended on age and meningococcal phenotype, the most pronounced seasonality being in 5-14-y-olds and in cases with phenotype C:2a:P1.2,5.

Adolescent↗
PubMed2005

Seasonal bone mass of college and senior female field hockey players.

AIM: The purpose of the study was to observe the relationship of field hockey playing with bone, muscle and fat in young and older adult women. METHODS: We measured body composition by dual energy X-ray absorptiometry (DXA) in college players, senior players and controls after a 4-month playing-season and 8-month off-season. Whole body (WB), proximal femur (PF), lumbar spine (LS), right and left forearm (RF, LF) bone mineral density (BMD), percent fat and lean mass of college players (20.6+/-1.1 years; 7.7+/-1 playing years) were compared with those of non-playing controls (19.5+/-1.5 years). BMD of senior players (37.3+/-10.3 years; 19.7+/-9.3 playing years) was compared to normative values. The differences between right and left forearm BMDs during the on and off seasons were also compared. RESULTS: College player BMD was higher than controls at the WB (p=0.02), PF (p=0.00004), RF (p=0.006) and LF (p=0.005), but not the LS. Senior player BMD was higher than age-matched norms at the WB (p=0.001) and PF (p=0.006), but not the LS, RF or LF. There were no differences between on and off-season BMDs for either group. There were no differences between college player RF and LF BMD in either season, nor in the senior players during the off-season, however, during the season, senior players developed greater RF than LF BMD (p=0.02). College players had greater lean mass (p=0.00008) and lower fat mass than controls (p=0.003). Neither changed significantly between seasons. Senior players lost fat (p=0.04) and gained lean mass (p=0.02) in season. CONCLUSION: Adult female field hockey players have higher than average bone mass that does not change significantly according to seasonal involvement.

Adult↗
PubMed2006

Seasonal variations in birth weights and gender of infants born in a mission hospital in Benin City, Nigeria.

OBJECTIVE: To examine the relationship, if any, between the geographical season in which a baby is born and the baby's birth weight and sex. METHODS: The birth weights and sexes of 6141 babies delivered over a five- year period in a Nigerian mission hospital were prospectively recorded according to the month and year of delivery. The mean birth weights and sexes of infants born in the wet season (May to October) were compared with those of their counterparts born in the dry season (November to April). RESULTS: Comparison of the mean birth weight during the wet and dry seasons showed that for male infants it was 3333 (542)g versus 3197 (566)g (p<0.01), while for female infants it was 3203 (559)g versus 3110 (601)g (p<0.01). When both sexes were combined, the mean birth weights were 3249 (488)g and 3164 (524)g in wet and dry seasons respectively(p<0.01). Slightly more boys than girls were born in the dry season compared with the wet season (p>0. 05). CONCLUSION: Irrespective of gender, babies born during the wet season were significantly heavier than their counterparts born during the dry season. There was a higher probability of a boy birth in the dry season.

Birth Weight↗
PubMed1991

Seasonal variation in growth during growth hormone therapy.

Seasonal variation in growth of normal children has been well described, although the mechanism by which it occurs has not been elucidated. The growth of 52 growth hormone-deficient children treated with synthetic human growth hormone was analyzed. A similar seasonal variation was observed, with mean (+/- SEM) peak growth occurring in the summer (8.2 +/- 0.3 cm/y) and winter (7.7 +/- 0.2 cm/y), and trough growth occurring in the autumn (6.9 +/- 0.3 cm/y). Forty-seven percent of subjects grew minimally during the autumn, and only two children showed peak growth in that season. Individual variations between maximal and minimal growth seasons amounted to 3.5 +/- 0.3 cm/y. The seasonal pattern was statistically significant for the group as a whole, for the prepubertal subgroup, and for the boys. The variation persisted when the first year of treatment was excluded to avoid bias of the initial growth spurt. The season of onset of therapy did not affect total growth during the first year. The demonstration of a seasonal pattern in growth of these children suggests that the seasonal variation may be mediated by peripheral rather than central factors. Paired clonidine-provoked growth hormone levels and an integrated concentration of 24-hour growth hormone levels and serum levels of insulinlike growth hormone I measured in a control group of normally growing children were also analyzed and showed no seasonal variation. This further suggests that peripheral rather than central factors are responsible for the seasonal variation in children's growth.

Adolescent↗
PubMed1994

Body mass index defines the risk of seasonal energy stress in the Third World.

A method has been devised to quantify the effect of seasonal environmental stress on nutritional well-being and to estimate the proportion of Third World populations at risk of functional deterioration. An Index of Agro-Climatic Seasonality, IACS--a measure of potential agricultural biomass availability--has been developed from agro-climatic data. IACS was found to be highly correlated with the seasonal weight loss of adults in rural Third World communities. This relationship was then used to predict the existence and severity of seasonal energy stress incurred by the adult population of Third World countries at any given body mass index (BMI). The average weight loss recorded in all seasonality studies was calculated; this value was used to specify, in combination with BMI, a condition of moderate seasonal energy stress. This grade of energy stress involved a loss of about 2% fat-free mass. The risk of greater energy stress, with larger losses of lean tissue, was specified as severe when predicted weight changes exceeded the maximum losses of weight recorded--at any given BMI--in Third World rural communities. The global dimensions of seasonality were then calculated by enumerating the individuals who--by the combined criteria of the BMI and the IACS of the habitat--fell into the categories of moderate and severe seasonality risk. On this basis, 65% of the rural adult population in the Third World run the risk of at least moderate seasonal energy stress, while 45% fall into the severe stress category. Of these 25% qualify as true seasonal 'casualties' because their body weight loss shifts their BMI from the normal range of nutritional status into the category of chronic energy deficiency.

Agriculture↗
PubMed1987

Seasonal effects on embryo transfer results in Brahman cows.

To determine factors affecting embryo donor reproductive performance in Bos indicus cows, 1,841 embryo collection records of 813 Brahman donor cows were analyzed using least-squares methods for unequal subclass numbers. The basic model included the main effects of either season or month, technician, and year of collection. Season and year did not affect (P>.10) the variance of number of ova collected. The most skillful technician collected 2.8 more ova per flush compared with the least skillful. Number of transferable embryos recovered per donor cow was affected by season (P<.06). Maximal recovery of transferable embryos occurred during the fall season (4.2) with a lower number (2.9) recovered during the winter season. Pregnancy rate in the recipients followed a seasonal pattern with lower (31.8%) pregnancy rates during the winter and higher (41.0%) ones in the fall. There was a trend toward higher pregnancy rates during February through October and lower rates December and January. Number of blastocysts recovered per donor was affected by season (P<.08), and year (P<.01). Number of blastocysts recovered per donor was lower (2.0) during the winter season than during the fall season (3.1). These data establish the concept of seasonal effects on embryo donor reproductive performance in Brahman cows.

Journal Article↗
PubMed1993

Comparing early embryo mortality in dairy cows during hot and cool seasons of the year.

The objectives of this study were to identify the level and stage of embryonic mortality that occur in dairy cows during hot and cool seasons of the year. Experimental dairy cows, of varying ages, were artificially inseminated with frozen-thawed semen from proven Holstein sires. Females on each dairy unit were then randomly allocated to one of three experimental groups after partitioning by day of artificial insemination, days post partum, parity, and current milk production level. In Group I and Group II, nonsurgical embryo collection was performed on each cow using Dulbecco's phosphate-buffered saline as the flushing medium. Embryos from cows in Group I were collected on Days 6 or 7 post insemination during the hot (n=93) and cool (n=64) seasons. Embryos from cows in Group II were collected on Days 13 or 14 post insemination during the hot (n=97) and cool (n=63) seasons. In Group III, contemporary control cows were also inseminated during the hot (n=106) and cool (n=106) seasons, and fetal heart beat was evaluated via ultrasound between Days 25 and 35 following insemination. Embryo viability decreased (P<0.05) from 59% at Day 7 to 27% at Day 14 in the hot season, but was not decreased during the cool season (52 vs. 60%). Pregnancy rate at Days 25 to 35 was 21% in the hot season, which was less (P<0.05) than the 36% in the cool season. The percentage of unfertilized ova collected in both the hot and cool seasons suggests that fertilization failure was not affected by season of breeding. In summary, embryonic loss after Day 7 of pregnancy appears to be a problem in this hot, dry climate.

Journal Article↗
PubMed1993

Modifications of PC20 and maximal degree of airway narrowing to methacholine after pollen season in pollen sensitive asthmatic patients.

We examined the effect of cessation of exposure to pollen on non-specific airway responsiveness in 10 grass and/or parietaria pollen sensitive asthmatics. Three methacholine inhalation challenges were performed, the first during pollen season (seasonal period), the second 2 months after the end of season (short time after seasonal period), and the third 5 months after the end of season (long time after seasonal period). The dose-response curves to methacholine were characterized by the PC20 (provocative concentration of methacholine required to produce a 20% fall in FEV1) and maximal response plateau, if possible. A maximal response plateau on the dose-response curve was considered to be present if three or more data points for FEV1 fell within a 5% response range. The challenge was stopped when FEV1 dropped more than 50% or the highest concentration of methacholine (200 mg/ml) was reached. The geometric mean (range) methacholine PC20 increased from 1.08 (0.18-37.22) in the seasonal period to 4.67 (0.71-200) mg/ml during the long time after seasonal period (P < 0.01). On the other hand, in six subjects in whom it was possible to obtain a plateau on at least one challenge, the level of the maximal response decreased from (mean +/- s.e.m.) 44.1 +/- 4.9 in the seasonal period to 30 +/- 4.4 during the long time after seasonal period (P < 0.05). These results suggest that in pollen sensitive asthmatic patients, the cessation of exposure to pollen is associated with a reduction of non-specific bronchial responsiveness (PC20 and maximal degree of airway narrowing to methacholine).

Adolescent↗
PubMed1993

Prevalence of seasonal affective disorder in Iceland.

OBJECTIVE: To investigate seasonal patterns in mood and behavior and estimate the prevalence of seasonal affective disorder (SAD) and subsyndromal seasonal affective disorder (S-SAD) in the Icelandic population. PARTICIPANTS AND SETTING: A random sample generated from the Icelandic National Register, consisting of 1000 men and women aged 17 to 67 years from all parts of Iceland. It represents 6.4 per million of the Icelandic population in this age group. DESIGN: The Seasonal Pattern Assessment Questionnaire, an instrument for investigating mood and behavioral changes with the seasons, was mailed to a random sample of the Icelandic population. The data were compared with results obtained with similar methods in populations in the United States. MAIN OUTCOME MEASURES: Seasonality score and prevalence rates of seasonal affective disorder and subsyndromal seasonal affective disorder. RESULTS: The prevalence of SAD and S-SAD were estimated at 3.8% and 7.5%, respectively, which is significantly lower than prevalence rates obtained with the same method on the east coast of the United States (chi 2 = 9.29 and 7.3; P < .01). The standardized rate ratios for Iceland compared with the United States were 0.49 and 0.63 for SAD and S-SAD, respectively. No case of summer SAD was found. CONCLUSIONS: Seasonal affective disorder and S-SAD are more common in younger individuals and among women. The weight gained by patients during the winter does not seem to result in chronic obesity. The prevalence of SAD and S-SAD was lower in Iceland than on the East Coast of the United States, in spite of Iceland's more northern latitude. These results are unexpected since the prevalence of these disorders has been found to increase in more northern latitudes. The Icelandic population has remained remarkably isolated during the past 1000 years. It is conceivable that persons with a predisposition to SAD have been at a disadvantage and that there may have been a population selection toward increased tolerance of winter darkness.

Adolescent↗
PubMed1993

The prevalence of seasonal affective disorder is low among descendants of Icelandic emigrants in Canada.

OBJECTIVE: To examine whether a genetic selection within the Icelandic population helps it to adapt to the long arctic winter. PARTICIPANTS AND SETTING: The target population was a group of adults in the Interlake district of Manitoba, Canada, wholly descended from Icelandic emigrants. The ancestry of every individual in this group can be traced back to 1840. DESIGN: The Seasonal Pattern Assessment Questionnaire was mailed to a random sample of the study population. The data were compared with results obtained with similar methods in populations in Iceland and on the eastern seaboard of the United States. MAIN OUTCOME MEASURES: Prevalence rates of seasonal affective disorder and subsyndromal seasonal affective disorder. RESULTS: The prevalence rates of seasonal affective disorder and subsyndromal seasonal affective disorder were found to be 1.2% and 3.3%, respectively, in this group of Canadians of wholly Icelandic descent. These are significantly lower than those measured with similar methods among people living along the east coast of the United States (chi 2 = 12.6 and 14.4, respectively, P < .001). Standardized rate ratio for this group compared with the American group was 0.18 for seasonal affective disorder and 0.38 for subsyndromal seasonal affective disorder. CONCLUSIONS: This is the second study to find the prevalence of seasonal affective disorder and subsyndromal seasonal affective disorder to be lower among Icelanders or their descendants than among populations along the east coast of the United States. The results indicate that the relationship between prevalence of these disorders and geographic latitude is more complex than has previously been suggested; genetic adaptation in Icelandic populations may play an important role.

Age Factors↗