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PubMed1982

Seasonality of pre-ovulatory non-disjunction and the aetiology of Down syndrome. A European collaborative study.

Six series of patients with Down syndrome (DS) from different European countries, altogether 287 cases, were divided into four categories according to parental origin of the additional chromosome 21 and meiotic division in which the nondisjunction had occurred. The monthly birth or conception frequencies per category were analysed by graph and compared with the total birth curve by Watson's adaptation of the Kolmogorov-Smirnov statistic for cyclic trends. Unexpectedly, the non-disjunctions during maternal meiosis I (63%), by far the largest category, occurred more frequently during the seasonal "restoration" and "inhibition" phase of the "ovulatory seasons" and less frequently when the ovulation rate is stabilized. The graph of the maternal meiosis II patients (17%) also seemed to conform to this phenomenon, though less obviously. In contrast to this, the paternal DS graph (20%) was very divergent, although a seasonal cluster of non-disjunctions may also occur here. From these findings a seasonal disturbance of preovulatory ripening of the ovum emerges as a possible cause of the first (and second) meiotic non-disjunction. Seasonal periodicity of the prolactin concentration in women and "transient hyperprolactinaemia", shown to be allied to delayed ovulation, may be related to these seasonal DS conception clusters.

Down Syndrome↗
PubMed1996

Seasonality of mortality in Sri Lanka: biometeorological considerations.

The seasonal variation of mortality in Sri Lanka was studied in relation to meteorological variables. Time series data of the total monthly number of deaths in men and women from 1976 to 1980 were analyzed by power spectrum analysis of the fast Fourier transformation method in the areas of Colombo (lowland area, altitude 7 m) and Nuwara-Eliya (highland area, altitude 1890 m), respectively. In the Colombo area, where the mean temperature was always high (mean, 27.5 degrees C), a seasonal variation in mortality of 6 months was validated by power spectrum analysis with peak times in June and November. These mortality peaks corresponded to those of the amounts of rainfall which also showed an identical predominant period of 6 months. In the Nuwara Eliya area, where the mean temperature was always low at about 15-16 degrees C, a seasonal variation of approximately 3 months was found in addition to the 6 months' periodicity. The comparison of the power spectrum pattern of mortality with those of meteorological variables suggested that the amount of rainfall was associated with the seasonal variation of mortality in the Nuwara-Eliya area. In conclusion, the seasonality of mortality in Sri Lanka, a typical tropical zone country, was related to seasonal variation in the amount of rainfall, or a humidity factor, but not to mean temperature.

Female↗
PubMed1990

Effects of nitrogen fertilizer treatment and source and season on grain quality of IR64 rice.

The effects of nitrogen fertilizer treatment and source (prilled urea, urea supergranule, fresh azolla, rice straw or sesbania or rice straw compost and their combinations) on grain quality were studied in the 1987 crops of variety IR64 at IRRI. Although fertilizer application improved grain yield, it improved protein content only in the case of urea supergranule, azolla and rice straw. Lysine contents of brown rice protein were similar in samples with no N fertilizer and those with the highest protein content in both seasons. Fertilizer treatment regardless of source tended to decrease weight and increase translucency of brown rice in both seasons. Effects on other grain properties were not consistent in both seasons. Season affected more grain properties than fertilizer treatment did, particularly translucency which was higher in the dry season than in the wet season.

Fertilizers↗
PubMed1992

The Zurich Study. XIV. Epidemiology of seasonal depression.

In a longitudinal cohort study of young adults from the Canton of Zurich in Switzerland (Zurich Study), seasonal patterns of several psychiatric and psychosomatic syndromes were investigated in two interviews over a period of three years. At an age of 27-28 years, 23% of the depressives, 15% of the neurasthenic subjects, and 14% of the subjects with backache reported an increased susceptibility in autumn and/or winter. With respect to the course we found that 10.4% of the subjects of the longitudinal sample (n = 417) suffered from seasonal depression (including individuals with subsyndromal seasonal difficulties) over two consecutive years. Specific symptoms, such as hypersomnia, increase of appetite or weight gain, were not found to be consistently associated with seasonal depression. A comparison of actual and retrospective reports on seasonal depression resulted in a very low reliability. In view of these results the seasonal subtype of depression should be diagnosed with caution, except when the diagnosis is based on longitudinal observations and/or external sources of information (e.g. family members, partner).

Adult↗
PubMed1992

Seasonal influences on gonadal and extragonadal sperm reserves in Small East African zebu (Bos indicus) bulls in Ethiopia.

Body weight and scrotal circumference (SC) data were taken ante mortem and genitalia collected after slaughter from Small East African zebu (SEAZ) bulls slaughtered during the wet (n = 46) and the dry (n = 53) seasons. Bulls slaughtered during the wet season were significantly heavier (47 kg) and had significantly larger SC measurements (3.3 cm) than those slaughtered during the dry season. Mean (+/- s.e.m.) paired testes weights were 233.7 +/- 13.8 and 292.8 +/- 11.3 g and epididymal weights 26.8 +/- 0.9 and 35.9 +/- 1.1 g in bulls slaughtered during the dry and wet seasons, respectively. Daily sperm production rates and epididymal sperm reserves were 2.2 +/- 0.1 x 10(9) and 3.0 +/- 0.1 x 10(9); and 16.1 +/- 0.3 x 10(9) and 17.6 +/- 0.4 x 10(9) in bulls slaughtered during the dry and wet seasons, respectively. These differences were significant. It was concluded that season affected reproductive capacity of zebu bulls probably due to variations in the quality and quantity of nutrition. However, the confounding effects of ambient temperature and nutrition on reproductive capacity of zebu bulls in tropical regions need further examinations.

Animals↗
PubMed2006

[Influenza vaccination in Germany. A population-based cross-sectional analysis of three seasons between 2002 and 2005].

BACKGROUND AND PURPOSE: Influenza represents a considerable worldwide health problem. Vaccination is the only preventive measure, capable of reducing mortality and morbidity of influenza in all age groups. The objective of this study was to assess the extent of influenza vaccination coverage in the seasons 2002/2003, 2003/2004 and 2004/2005 in Germany, to understand the driving forces and barriers to vaccination, and to determine vaccination intentions for the subsequent winter. METHODS: The authors conducted a random-sampling, telephone-based household survey among noninstitutionalized individuals representative of the population aged > or =14. The surveys for the different seasons used the same questionnaire and were subsequently pooled. Four target groups were determined for analysis: (1) persons aged > or =60; (2) people working in the medical field; (3) persons suffering from chronic illness; and (4) a composite group made up of persons aged > or =60 or working in the medical field or suffering from a chronic illness. RESULTS: The overall sample consisted of 5,990 people. The influenza vaccination coverage rate in Germany increased from 22.3% in season 2002/2003 to 25.1% in season 2003/2004 and increased again to 26.5% in season 2004/2005. This increase is statistically significant (p = 0.007). The composite group coverage rate increased from 40.0% (2002/2003) to 42.2% (2004/2005). The driving forces and barriers to vaccination did not change over the years. The most frequent reasons for being vaccinated given by vaccinees were: influenza considered to be a serious illness which people wanted to avoid, having received advice from the family doctor or nurse to be vaccinated, and not wanting to infect family and friends. Reasons for not being vaccinated mentioned by people who have never been vaccinated were: thinking about it, however, not being vaccinated in the end, not expecting to catch influenza, and not having received a recommendation from the family doctor to be vaccinated. Major encouraging factors to influenza vaccination were: recommendation by the family doctor or nurse, more available information on the vaccine regarding efficacy and tolerance, and more information available about the disease. CONCLUSION: The vaccination coverage rate increased by 4.2% over the three seasons. The family doctor is the most important source of encouragement for people to be vaccinated against influenza. It seems that the public would be more likely to be vaccinated if they had more information on the efficacy and tolerance of the vaccine, as well as the disease. The authors therefore suggest that family doctors be better informed on influenza vaccine and the disease itself, so that they can actively inform their patients on these topics.

Adolescent↗
PubMed2001

The effect of season and vitamin D supplementation on bone mineral density in healthy women: a double-masked crossover study.

Vitamin D status is known to be an important determinant of bone mineral density (BMD). There is a significant seasonal variation in serum vitamin D, and some studies have reported an associated seasonal variation in BMD. The present study was devised to investigate whether a seasonal variation in BMD could be detected in healthy normal subjects, along with associated variations in serum parathyroid hormone (PTH), intestinal calcium absorption and biochemical markers of bone turnover. A second aim was to investigate whether, if such variations were identified, they could be suppressed by vitamin D supplementation. The subjects were 70 healthy female volunteers (mean age 47.2 years, range 24-70 years) recruited into a double-masked crossover study and followed over 2 years. During the first year 35 subjects received a daily oral supplement containing 800 IU (20 micrograms) cholecalciferol (group 1) and 35 subjects received a placebo preparation (group 2). During the second year the treatment each group received was reversed. Lumbar spine (L1-L4), left proximal femur and total body BMD were measured by DXA at 3-month intervals. Serum 25-hydroxyvitamin D (25-OHD), serum PTH, bone markers (bone-specific ALP (BSAP) and urinary crosslinks (DYPD/creatinine)) and calcium absorption were also measured at each visit. Cholecalciferol treatment increased serum 25-OHD by 25.4 nmol/l (p < 0.001), while a reciprocal decrease in serum PTH of 6.6 ng/l (p = 0.011) was seen in subjects in the lowest quartile of baseline serum 25-OHD. The treatment had no significant effect on spine, femur or total body BMD, calcium absorption or bone markers. When Fourier analysis was used to analyze the data for seasonal effect (defined as twice the amplitude of the 1-year period variation) a highly significant effect for 25-OHD of 18 nmol/l (p < 0.001) was found. However, no effect was found for BMD, PTH, calcium absorption or bone markers. The analysis set a 95% confidence limit to the seasonal effect of less than 0.6% for spine, total hip and total body BMD. It was concluded that in the population of healthy women studied there was no evidence of seasonal variation in spine, femur or total body BMD, serum PTH, calcium absorption or bone markers. Vitamin D supplementation was found to have no effect on BMD.

Adult↗
PubMed2005

Regulation and seasonal dynamics of extracellular enzyme activities in the sediments of a large lowland river.

We tested whether seasonal changes in the sources of organic substances for microbial metabolism were reflected changes in the activities of five extracellular enzymes in the eighth order lowland River Elbe, Germany. Leucine aminopeptidase showed the highest activities in the water column and the sediments, followed by phosphatase > beta-glucosidase > alpha-glucosidase > exo-1,4-beta-glucanase. Individual enzymes exhibited characteristic seasonal dynamics, as indicated by their relative contribution to cumulative enzyme activity. Leucine aminopeptidase was significantly more active in spring and summer. In contrast, the carbohydrate-degrading enzymes peaked in autumn, and beta-glucosidase activity peaked once again in winter. Thus, in sediments, the ratio of leucine aminopeptidase/beta-glucosidase reached significant higher medians in spring and summer (5-cm depth: ratio 7.7; 20-cm depth: ratio 10.1) than in autumn and winter (5-cm depth: ratio 3.7, 20-cm depth: ratio 6.3). The relative activity of phosphatase in the sediments was seasonally related to both the biomass of planktonic algae as well as to the high content of total particulate phosphorus in autumn and winter. Due to temporal shifts in organic matter supply and changes in the storage capacity of sediments, the seasonal peaks of enzyme activities in sediments exhibited a time lag of 2-3 months compared to that in the water column, along with a significant extension of peak width. Hence, our data show that the seasonal pattern of extracellular enzyme activities provides a sensitive approach to infer seasonal or temporary availability of organic matter in rivers from autochthonous and allochthonous sources. From the dynamics of individual enzyme activities, a consistent synoptic pattern of heterotrophic functioning in the studied river ecosystem could be derived. Our data support the revised riverine productivity model predicting that the metabolism of organic matter in high-order rivers is mainly fuelled by autochthonous production occurring in these reaches and riparian inputs.

Enzymes↗
PubMed2005

Consensus Seasonal Flood Forecasts and Warning Response System (FFWRS): an alternate for nonstructural flood management in Bangladesh.

Despite advances in short-range flood forecasting and information dissemination systems in Bangladesh, the present system is less than satisfactory. This is because of short lead-time products, outdated dissemination networks, and lack of direct feedback from the end-user. One viable solution is to produce long-lead seasonal forecasts--the demand for which is significantly increasing in Bangladesh--and disseminate these products through the appropriate channels. As observed in other regions, the success of seasonal forecasts, in contrast to short-term forecast, depends on consensus among the participating institutions. The Flood Forecasting and Warning Response System (henceforth, FFWRS) has been found to be an important component in a comprehensive and participatory approach to seasonal flood management. A general consensus in producing seasonal forecasts can thus be achieved by enhancing the existing FFWRS. Therefore, the primary objective of this paper is to revisit and modify the framework of an ideal warning response system for issuance of consensus seasonal flood forecasts in Bangladesh. The five-stage FFWRS-i) Flood forecasting, ii) Forecast interpretation and message formulation, iii) Warning preparation and dissemination, iv) Responses, and v) Review and analysis-has been modified. To apply the concept of consensus forecast, a framework similar to that of the Southern African Regional Climate Outlook Forum (SARCOF) has been discussed. Finally, the need for a climate Outlook Fora has been emphasized for a comprehensive and participatory approach to seasonal flood hazard management in Bangladesh.

Bangladesh↗
PubMed1997

[Rhegmatogenous retinal detachments. Seasonal variation and incidence].

UNLABELLED: Seasonal variations in the relative incidence of rhegmatogenous retinal detachment were reported as a trend in several studies on the database of relatively limited cohort sizes. PATIENTS AND METHODS: An analysis on this topic was performed with a long-term database. A total of 3073 files of patients with rhegmatogenous retinal detachment, covering 11 years of observation, were reviewed for this study. Patients with signs of long-standing detachment or other predisposing diseases were excluded, so that a basic study population of 2314 patients remained for the analysis. RESULTS: The averaged seasonal incidence of rhegmatogenous detachments revealed a significant (P < 0.005) mid-summer peak (n in July = 228) and a winter trough (mean of December-January = 161; difference = 36%). Phase and curve fitting of the seasonal variations in the number of retina detachment cases was similar to the seasonal variation of the astronomic duration of the day (P < 0.001). The relation was closer compared to the average duration of light exposure per day calculated from behavioural data and the astronomic length of light phase (P < 0.0002). CONCLUSION: This long-time study revealed a close correlation of the relative seasonal incidence of retinal detachment and the seasonal variation of light hours per day. So far, this observations cannot be explained pathogenetically. Two basic hypotheses ought to be investigated further: (1) The influence of light on the generation of toxic oxygen radicals and the subsequent destruction of the vitreous and (2) possible light-induced changes in vitreoretinal adhesion.

Adult↗
PubMed2006

Seasonal variation in avian auditory evoked responses to tones: a comparative analysis of Carolina chickadees, tufted titmice, and white-breasted nuthatches.

We tested for seasonal plasticity of the peripheral auditory system of three North American members of the Sylvioidea: Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis). We measured three classes of auditory evoked responses (AER) to tone stimuli: sustained receptor/neural responses to pure-tone condensation waveforms, the frequency-following response (FFR), and the earliest peak of the AER to stimulus onset (tone onset response). Seasonal changes were detected in all classes of AERs in chickadees and nuthatches. Seasonal changes in titmice were restricted to the tone onset response. Interestingly, changes detected in chickadees (and to a lesser extent in titmice) were generally in an opposite direction to changes seen in nuthatches, with chickadees exhibiting greater amplitude AER responses in the spring than in winter, and nuthatches exhibiting greater amplitude AER responses in winter than in spring. In addition, the seasonal differences in the sustained responses tended to be broad-band in the chickadees but restricted to a narrower frequency range in nuthatches. In contrast, seasonal differences in the onset response were over a broader frequency range in titmice than in chickadees and nuthatches. We discuss some possible mechanistic and functional explanations for these seasonal changes.

Acoustic Stimulation↗
PubMed2006

Seasonal variation in the metabolic rate and body composition of female grey seals: fat conservation prior to high-cost reproduction in a capital breeder?

Many animals rely on stored energy through periods of high energy demand or low energy availability or both. A variety of mechanisms may be employed to attain and conserve energy for such periods. Wild grey seals demonstrate seasonal patterns of energy storage and foraging behaviour that appear to maximize the allocation of energy to reproduction--a period characterized by both high energy demand and low food availability. We examined seasonal patterns in resting rates of oxygen consumption as a proxy for metabolic rate (RMR) and body composition in female grey seals (four adults and six juveniles), testing the hypothesis that adults would show seasonal changes in RMR related to the reproductive cycle but that juveniles would not. There was significant seasonal variation in rates of resting oxygen consumption of adult females, with rates being highest in the spring and declining through the summer months into autumn. This variation was not related to changes in water temperature. Adults increased in total body mass and in fat content during the same spring to autumn period that RMR declined. RMR of juveniles showed no clear seasonal patterns, but did increase with increasing mass. These data support the hypothesis that seasonal variation in RMR in female grey seals is related to the high costs of breeding.

Adipose Tissue↗
PubMed2000

Seasonal changes in plasma testosterone and glucocorticosteroids in free-living male yellow-pine chipmunks and the response to capture and handling.

We measured plasma levels of testosterone, corticosterone, and cortisol in free-living male yellow-pine chipmunks to demonstrate the patterns of seasonal variation and to assess the effects of capture and handling on hormone levels. We achieved the latter by modifying our standard trapping technique (blood samples collected within 1-3 h of capture) to obtain blood samples that allowed measurement of hormone levels within 3 min of capture (basal) and again 30 min later. By alternating the modified and standard trapping techniques over 7 months of the active season we demonstrated that seasonal patterns of variation in steroid hormone levels can be accurately described with the simpler, standard trapping technique. Basal and 30-min post-capture testosterone levels were high during mating and dropped to a persistently low level thereafter. Conversely, both cortisol and corticosterone were at their seasonal low during mating and climbed to peak levels in June following reproduction. Plasma glucocorticosteroid levels increased during the 30 min after capture and handling at all times of the active season, and these elevated levels were similar to the levels obtained by standard trapping. Testosterone levels during the mating period also increased in response to capture and handling. The contrasting patterns of seasonal variation in glucocorticosteroid and testosterone levels and the changes induced by capture and handling suggest that when testosterone concentration is high, adrenocortical activity is suppressed.

Animals↗
PubMed2004

Histological organization of roe deer testis throughout the seasonal cycle: variable and constant components of tubular and interstitial compartment.

Seasonally regulated breeding in roe deer, Capreolus capreolus, is associated with significant changes in testis mass, structure and function. This study has quantified seasonal changes of morphometric parameters and cellular composition in roe deer testis parenchyma. Tissue samples were collected bimonthly during a complete annual cycle. Morphometric parameters of seminiferous tubules were measured and the number of different cell types was counted using a computer-aided image-analyzing system. A scheme of eight tubular epithelium stages for active spermatogenesis was devised according to the spermatid development. Stage I is characterized by the occurrence of new round spermatids, stage IV by spermiation and stage VIII by the meiotic division of spermatocytes. The average diameter of seminiferous tubules varied between 88.4+/-3.6 micro m (February) and 216.8+/-9.2 micro m (June). Also numbers of spermatogonia, spermatocytes and spermatids per tubule cross-section showed considerable seasonal changes. In December and February the germinative epithelium mainly consists of Sertoli cells and spermatogonia. In February, the first differentiated spermatogonia enter meiosis, and in April even spermatids occasionally occur, which reach their highest numbers during the rut in August. Both the expansion and the proportion of tubular and interstitial compartment change seasonally and result in differing cell densities. Assuming numerically constant populations of Sertoli cells and interstitial cells during the entire year, the hypothetical cell numbers per mm(2) of the tubular and interstitial areas were calculated for the seasonally variable total areas of tissue cross-sections. The concordance of these theoretical values with measured cell densities provided evidence that the total numbers of Sertoli cells, as well as interstitial cells, remain really constant throughout the seasonal cycle. The exact quantification of variable and constant components provides basic data for characterization of cell type and stage-specific processes of spermatogenesis.

Animals↗
PubMed1997

ACP1 and human adaptability. 2. Association with season of conception.

We have studied the pattern of association between the season of conception and cytosolic low molecular weight phosphotyrosine phosphatase (ACP1) genetic polymorphism in 329 consecutively newborn infants from the population of Penne and 361 consecutively newborn infants from the population of Rome. In addition, 329 mothers were studied in the population of Penne. A concordant, highly significant association was observed in the two populations between ACP1 parameters and the season of conception of newborn infants. The total activity of ACP1 shows a minimum in infants conceived in January-February and a maximum in those conceived at the end of the solar year. Analysis of the joint mother-newborn ACP1 distribution in relation to the season of fertilisation has shown that among mothers carrying ACP1*A (the allele showing the lowest activity), the proportion of newborns carrying this allele is higher in those conceived in the first months of the year than in those conceived subsequently. Since ACP1 probably functions as a phosphotyrosine phosphatase and as a flavin mononucleotide phosphatase, low activity could enhance the metabolic rate and would be advantageous in a cold environment. The cycle of variation of ACP1 in infants follows the cycle of solar illumination. It is possible that individuals who have a genetic background allowing them to adapt easily and readily to seasonal demand are more successful in reproducing themselves. The population of zygotes conceived in a given season would therefore reproduce the pattern of gene combination more fit for that season.

Acclimatization↗
PubMed2006

Seasonal, daily and diurnal variations in the stable carbon isotope composition of carbon dioxide respired by tree trunks in a deciduous oak forest.

The stable C isotope composition (delta13C) of CO2 respired by trunks was examined in a mature temperate deciduous oak forest (Quercus petraea). Month-to-month, day-to-day and diurnal, measurements were made to determine the range of variations at different temporal scales. Trunk growth and respiration rates were assessed. Phloem tissue was sampled and was analysed for total organic matter and soluble sugar 13C composition. The CO2 respired by trunk was always enriched in 13C relative to the total organic matter, sometimes by as much as 5 per thousand. The delta13C of respired CO2 exhibited a large seasonal variation (3.3 per thousand), with a relative maximum at the beginning of the growth period. The lowest values occurred in summer when the respiration rates were maximal. After the cessation of radial trunk growth, the respired CO2 delta13C values showed a progressive increase, which was linked to a parallel increase in soluble sugar content in the phloem tissue (R=0.95; P<0.01). At the same time, the respiration rates declined. This limited use of the substrate pool might allow the discrimination during respiration to be more strongly expressed. The late-season increase in CO2 delta13C might also be linked to a shift from recently assimilated C to reserves. At the seasonal scale, CO2 delta13C was negatively correlated with air temperature (R=-0.80; P<0.01). The diurnal variation sometimes reached 3 per thousand, but the range and the pattern depended on the period within the growing season. Contrary to expectations, diurnal variations were maximal in winter and spring when the leaves were missing or not totally functional. By contrast to the seasonal scale, these diurnal variations were not related to air temperature or sugar content. Our study shows that seasonal and diurnal variations of respired 13C exhibited a similar large range but were probably explained by different mechanisms.

Analysis of Variance↗
PubMed1999

Monthly trend and seasonal variation in twinning rate in Japan, 1975-1994.

We examined birth records from Japanese statistics, 1975-1994, to investigate the seasonality of twin births. We could identify 198,924 pairs of twins (97.9% of all the registered twin records) and estimated the numbers of mono- and dizygotic twin pairs. The seasonal index of the twinning rate for each month was calculated by dividing the crude rate by the estimated trend value for the month. There were significant variations in the seasonal index for overall, dizygotic and monozygotic twinning rates. Peak months with values more than 3% higher than expected were July and October-December for dizygotic twins, and April and June for monozygotic twins; these seasonalities were statistically significant by analysis of variance and the patterns were similar in recent years, with a sharp increase in the total twinning rate. When observed year-by-year, however, there were years that did not show these typical seasonalities. It is suggested that the mechanisms for probable seasonal variations in twinning rates are different for dizygotic and monozygotic twin pregnancies, and that factors involved in these variations are not effective every year.

Adult↗
PubMed2004

Estimation of seasonal variations in risk factor profiles and mortality from coronary heart disease.

OBJECTIVE: Seasonal variations in coronary heart disease (CHD) and related risk factors have been reported previously. However, no studies to date quantify the contribution of seasonal variations in risk factors to actual mortality in both men and women using a single database of sufficient size and follow-up. METHODS: We investigated the database from the Western Austrian Vorarlberg Health Monitoring and Promotion Programme (VHM&PP) including over 450,000 repeated measurements of 149,650 individuals between 1985 and 1999. RESULTS: Of a total of 1266 deaths from CHD (ICD-9 410-414), 353 deaths occurred between December and February (27.9%), in contrast to 275 (21.7%) between June and August. While the frequency of deaths through acute myocardial infarction (ICD-9 410) was similar over the seasons, chronic forms of CHD (ICD-9 414) occurred significantly (p < 0.001) more frequently in winter. Total cholesterol, blood pressure and body mass index showed pronounced seasonal variations with average levels significantly higher during the winter months in all age groups and both sexes, giving an estimated increase in score risk of 6.8% in men and 3.6% in women. However by contrast, use of single time point risk factor data tended to over-estimate subsequent 10 year mortality if measured in winter and the converse in summer. CONCLUSION: For the first time, this study quantifies the contribution of seasonal risk factor variation to CHD mortality. The consistent effect across demographic groups suggests that this is a real physiological phenomenon and not an artefact of living conditions. Interpretation of standard risk scores should take account of this seasonal fluctuation in subsequent investigation and follow-up.

Adult↗