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PubMed2002

Seasonal variations in clinical and laboratory variables among chronic hemodialysis patients.

Seasonal variations in BP among chronic hemodialysis patients have been reported. It was hypothesized that other characteristics of these patients might also vary with the seasons. Twenty-one clinical and laboratory variables were examined for seasonal variations among 1445 patients enrolled in the Hemodialysis Study, sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases. Mixed-effects models were applied to longitudinal changes (up to 45 mo) for individual patients for 19 of the 21 variables, which were measured at least twice each year, to determine the seasonal component of each variable. Seasonal variations in the other two variables, i.e., protein and energy intakes determined from annual dietary records, were assessed in cross-sectional comparisons of intakes of patients entering the study at different time points. Thirteen of the 21 variables examined demonstrated statistically significant (P < 0.01) seasonal components in their longitudinal variations. Predialysis blood urea nitrogen concentrations peaked in March, which coincided approximately with the peak protein catabolic rates, as well as protein and energy intakes (determined by dietary recall). Predialysis systolic and diastolic BP values were highest in winter and lowest in summer, corroborating previous reports. In addition, the lower predialysis BP values in summer were associated with higher outdoor temperatures and less interdialytic fluid gain. The mean predialysis hematocrit values were highest in July, which could not be attributed solely to the estimated changes in plasma volume. Seasonal variations in clinical and laboratory variables occur commonly among chronic hemodialysis patients. The reasons for most of these variations are not apparent and require further investigation. Nonetheless, failure to consider these variations might lead to biases in the interpretation of clinical studies. In addition, awareness of these variations might facilitate the interpretation of laboratory results and the clinical treatment of these patients.

Adult↗

PubMed2002

A seasonal variation in breast cancer.

AIM: To demonstrate a seasonal variation in the detection of breast cancer in women diagnosed at St Marks Breast Centre, Auckland. METHODS: Data on women diagnosed with breast cancer at St Marks Breast Centre from January 1992 till December 2001 were obtained from the computerised database. RESULTS: A total of 1760 women were diagnosed with breast cancer; 1584 were referred by their general practitioner and 176 self referred. The peak incidence of seasonal diagnosis was in spring (September, October, November) with 521 cases. The lowest incidence was in summer (December, January, February) with 375 cases. These findings were consistent annually from 1992 to 2001. CONCLUSIONS: There is a seasonal variation in the incidence of breast cancer similar to that noted in other studies. Our findings suggest that temporal factors and possible behavioural patterns may have a role in this seasonal variation.

Breast Neoplasms↗

PubMed1993

Absence of seasonal variation in malaria parasitaemia in an area of intense seasonal transmission.

Parasitological surveys carried out in two villages of the Kilombero district of Tanzania indicated a very high prevalence of Plasmodium falciparum parasitaemia throughout the year (all ages mean prevalence = 69.2%) and a low, unstable prevalence of P. malariae (all ages mean prevalence = 4.5%). Fevers (temperature > or = 37.5 degrees C) in both children and adults showed irregular changes in prevalence over time, but there was no seasonal pattern. Neither was there seasonal variation in either P. falciparum parasite prevalence or parasite densities. This was despite marked seasonality in vectors caught in CDC light-traps and in estimated sporozoite inoculations determined by ELISA. The estimated mean annual inoculation rate was extremely high, over 300 infectious bites per person per year, the main vectors being members of the A. gambiae complex and Anopheles funestus. There was considerable variation between houses but even in houses with relatively low mosquito numbers the inoculation rate was sufficient to maintain a maximal P. falciparum prevalence. Heterogeneities in exposure cannot explain why the parasite prevalence is not always 100%. In areas of such high transmission, parasitaemias are likely to be determined mainly by the interaction of schizogony and anti-blood stage immunity, since parasites arising from new inoculations generally comprise only a small proportion of the total in the circulation. In any one individual, this will lead to periodic fluctuations in levels of parasitaemia. These are unlikely to show a close relationship to either seasonal variation in inoculations or to differences between households in the local inoculation rate.

Adolescent↗

PubMed2004

Seasonal variation in hospitalization and case fatality of subarachnoid hemorrhage - a nationwide danish study on 9,367 patients.

Seasonal variation in the occurrence of cerebrovascular disease has been reported, but data about subarachnoid hemorrhage (SAH) are few and inconclusive. We conducted a nationwide population-based study in Denmark to examine any seasonal pattern of hospitalization and case fatality of SAH. We identified 9,367 patients with SAH and found a modest indication of overall seasonal variation for the risk of hospitalization with this diagnosis. The seasonal pattern, with the highest incidence in January and the nadir in July, was mostly apparent for subjects aged >65 years (peak-to-trough ratio = 1.18; 95% CI 1.04-1.32). There was little difference by sex. The overall 30-day case fatality rate was 38% and showed less seasonal variation. We found evidence of weak seasonal variation in hospitalization for SAH and almost no seasonal variation in a 30-day case fatality rate after SAH.

Age Factors↗

PubMed1999

Seasonal variations in the diagnosis of childhood cancer in the United States.

Seasonal trends in month of diagnosis have been reported for childhood acute lymphoblastic leukaemia (ALL) and non-Hodgkin's lymphoma (NHL). This seasonal variation has been suggested to represent an underlying viral aetiology for these malignancies. Some studies have shown the highest frequency of diagnoses in the summer months, although this has been inconsistent. Data from the Children's Cancer Group and the Pediatric Oncology Group were analysed for seasonal incidence patterns. A total of 20,949 incident cancer cases diagnosed in the USA from 1 January 1989 through 31 December 1991 were available for analyses. Diagnosis-specific malignancies available for evaluation included ALL, acute myeloid leukaemia (AML), Hodgkin's disease, NHL, rhabdomyosarcoma, neuroblastoma, retinoblastoma, osteosarcoma, Wilms' tumour, retinoblastoma, Ewings' sarcoma, central nervous system (CNS) tumours and hepatoblastoma. Overall, there was no statistically significant seasonal variation in the month of diagnosis for all childhood cancers combined. For diagnosis-specific malignancies, there was a statistically significant seasonal variation for ALL (P = 0.01; peak in summer), rhabdomyosarcoma (P = 0.03; spring/summer) and hepatoblastoma (P = 0.01; summer); there was no seasonal variation in the diagnosis of NHL. When cases were restricted to latitudes greater than 40 degrees ('north'), seasonal patterns were apparent only for ALL and hepatoblastoma. Notably, 33% of hepatoblastoma cases were diagnosed in the summer months. In contrast, for latitudes less than 40 degrees ('south'), only CNS tumours demonstrated a seasonal pattern (P = 0.002; winter). Although these data provide modest support for a summer peak in the diagnosis of childhood ALL, any underlying biological mechanisms that account for these seasonal patterns are likely complex and in need of more definitive studies.

Adolescent↗

PubMed1988

An analysis of the seasonal variation of coronary heart disease and respiratory disease mortality in New Zealand.

The seasonal variation of coronary heart disease mortality rates in New Zealand is analysed by age, sex and race using monthly national mortality data for the period 1970-83. A 35% variation from the winter peak to summer low is found in the crude mortality rate, but the size of the seasonal variation is age-dependent, being more pronounced in the elderly, and more so in males than in females. The hypothesis that respiratory infections are linked to coronary heart disease, and that their seasonal occurrence explains the seasonal variation in coronary rates, is examined by an analysis of the association between coronary disease and respiratory disease mortality rates. By partial correlation analysis and by examining the residual correlation after filtering the seasonal variation from both series, it is suggested that the season acts as a confounding factor to cause an apparent association between the two rates. After controlling for season there is a tenuous relationship, but it is apparent only in the elderly.

Adult↗

PubMed2002

Seasonal variation of P-wave dispersion in healthy subjects.

We studied the seasonal variability of P dispersion in 523 healthy male patients, aged 22 +/- 4 years (range, 20-26). Four seasonal 12-lead resting electrocardiograms were recorded at 2 mV/cm standardization and at 50 mm/s paper speed at intervals of three months. Electrocardiograms were recorded between the hours 10 to 12 AM. The difference between the maximum P-wave duration and minimum P-wave duration was calculated and defined as "P dispersion." There was a significant seasonal variation in the maximum P-wave duration (P = .001) and P dispersion (P = .001), with the longest maximum P-wave duration (121 +/- 16 ms) and P dispersion (41 +/- 7 ms) observed in winter and the shortest maximum P-wave duration (106 +/- 15 ms) and P dispersion (24 +/- 8 ms) observed in summer. The minimum P-wave duration did not show any significant seasonal variation. In conclusion, there exists a significant seasonal variation in the maximum P-wave duration and P dispersion in healthy patients. Seasonal variation of P dispersion resulted from the significant variation of maximum P-wave duration.

Adult↗

PubMed2001

Seasonal variation in acute intestinal vasculopathy mortality in France.

OBJECTIVES: Seasonal and circadian rhythms are observed in cardiovascular diseases. Seasonal variation in acute intestinal vasculopathy has never been investigated. This report describes the seasonal variation of acute intestinal vasculopathy mortality in the French population. METHODS: All deaths that occurred among French adults over the period 1987-1996 (N = 20,830) for acute intestinal vasculopathy (International Classification of Diseases, Ninth Revision code 557.0) were examined retrospectively. Cumulated monthly averages were expressed as the percentage above or below the average monthly value during the entire study period. RESULTS: Deaths for acute intestinal vasculopathy peaked in January (15% above the trend), and were lowest in July (11% below the trend), both in the overall population (Roger's test: p < 0.001) and in subgroups defined by age (>69 yr old) and sex. Compared to other subgroups, the >90 yr old individuals had a higher incidence of acute intestinal vasculopathy with a greater amplitude of seasonal variation (p < 0.001). CONCLUSIONS: Awareness of higher risk during winter would help to reduce the high mortality from acute intestinal vasculopathy. A better understanding of this seasonal pattern would allow practitioners to improve early diagnosis and treatment.

Acute Disease↗

PubMed2005

Seasonal variations of phenolic compounds in Australia-grown tea (Camellia sinensis).

Seasonal variations of phenolic compounds in fresh tea shoots grown in Australia were studied using an HPLC method. Three principal tea flavanols [epigallocatechin gallate (EGCG), epicatechin gallate (ECG), and epigallocatechin (EGC)] and four grouped phenolics [total catechins (Cs), total catechin gallates (CGs), total flavanols (Fla), and total polyphenols (PPs)] in fresh tea shoots were analyzed and compared during the commercial harvest seasons from April 2000 to May 2001. The levels of EGCG, ECG, and CGs in the fresh tea shoots were higher in the warm months of April 2000 (120.52, 34.50, and 163.75 mg/g, respectively) and May 2000 (128.63, 44.26, and 183.83 mg/g, respectively) and lower during the cool months of July 2000 (91.39, 35.16, and 132.30 mg/g, respectively), August 2000 (91.31, 31.56, and 128.64 mg/g, respectively), and September 2000 (96.12, 33.51, and 136.90 mg/g, respectively). Thereafter, the levels increased throughout the warmer months from October to December 2000 and remained high until May 2001. In the warmer months, the levels of EGCG, ECG, and CGs were in most cases significantly higher (P < 0.05) than those in the samples harvested in the cooler months. In contrast, the levels of EGC and Cs were high and consistent in the cooler months and low in the warmer months. The seasonal variations of the individual and grouped catechins were significant (P < 0.05) between the cooler and warmer months. This study revealed that EGCG and ECG could be used as quality descriptors for monitoring the seasonal variations of phenolics in Australia-grown tea leaves, and the ratio (EGCG + ECG)/EGC has been suggested as a quality index for measuring the differences in flavanol levels in fresh tea shoots across the growing seasons. Mechanisms that induce seasonal variations in tea shoots may include one or all three of the following environmental conditions: day length, sunlight, and/or temperature, which vary markedly across seasons. Therefore, further studies under controlled conditions such as in a greenhouse may be required to direct correlate flavonoid profiles of green tea leaves with their yields and also to with conditions such as rainfall and humidity.

Australia↗

PubMed1996

Diarrhoea associated with Candida spp.: incidence and seasonal variation.

To study the incidence and seasonal variation of diarrhoea associated with Candida, 978 diarrhoeal stool specimens from patients of all age groups were examined by microscopy and culture. Candida spp. was the sole pathogen (unassociated with other diarrhoeagenic bacteria, protozoa, or helminths) in 15.3% of the total cases. Candida albicans (94.9%) was the predominant species isolated. The incidence was highest among the infants aged 0-12 months (37.1%), followed by a decline in the rest of the children aged less than 5 years with a second peak in the people aged over 5 years, including adults. The paediatric age group had a significantly higher incidence in the summer season compared to the rainy (p < 0.05) or winter (p < 0.01) months. Thus, there was a definite age and seasonal variation in the incidence of diarrhoea caused by the overgrowth of Candida in the Varanasi region of the Indian subcontinent.

Adolescent↗

PubMed1997

Seasonal variation in fibrinogen in the Rotterdam Study.

As evidence accumulates to implicate fibrinogen as a risk indicator for cardiovascular disease, it is of interest to study its seasonal variation. A population based cross-sectional study was performed among participants of the Rotterdam Study, a cohort of 7,983 men and women, aged 55 years and over. Fibrinogen levels were measured by the prothrombin time derived method in the first 2,325 participants of the study. Fibrinogen levels were considerably higher in winter. The seasonal difference was 0.34 g/l (95% confidence interval 0.29, 0.39) and was more pronounced in subjects aged 75 years and over than in subjects aged 55 to 75 years, 0.43 g/l (0.34, 0.52) and 0.29 g/l (0.24, 0.35), respectively. Additional adjustment for body mass index, systolic and diastolic blood pressure, and total and HDL cholesterol did not materially change the findings. After adjustment for seasons, outdoor temperature was not associated with fibrinogen. Adjustment for outdoor temperature did not change the seasonal variation of fibrinogen, seasonal difference 0.31 g/l (0.24, 0.37). In conclusion, fibrinogen levels are highest in Winter. The seasonal variation of fibrinogen is more pronounced in the elderly. Outdoor temperature does not seem to play a role in the seasonal variation of fibrinogen. Seasonal variation of fibrinogen may partly explain the increased cardiovascular disease mortality in Winter.

Adult↗

PubMed1993

Seasonal variation of blood pressure and its relationship to ambient temperature in an elderly population.

OBJECTIVE: To measure the magnitude and timing of seasonal variation of blood pressure and related factors in the elderly living in the community, and to assess their potential impact on cardiovascular risk. DESIGN: Prospective study; from January 1991 to February 1992 blood pressure and other variables were measured at 2-monthly intervals in each subject in their own homes. SUBJECTS: Ninety-six men and women, age range 65-74 years, recruited from a single group general practice in Cambridge. MAIN OUTCOME MEASURES: Seasonal variation of blood pressure, seasonal variation of prevalence of hypertension, seasonal variation of ambient temperature and body mass index. RESULTS: Both systolic (SBP) and diastolic blood pressure (DBP) were greatest during the winter across the whole distribution of blood pressure. There was a fourfold increase in the proportion of subjects with blood pressures > 160/90 mmHg in winter compared with in summer. Regression analysis revealed highly significant seasonal differences in both SBP and DBP. After adjustment for confounding seasonal effects, a 1 degree C decrease in living-room temperature was associated with rises of 1.3 mmHg in SBP and 0.6 mmHg in DBP. CONCLUSIONS: Seasonal variation of blood pressure is heightened in older adults and may partly explain the greater cardiovascular disease mortality of elderly subjects during the winter. The blood pressures of elderly people may be inversely related to the ambient temperature. The public health implications of these findings deserve further investigation.

Aged↗

PubMed2003

Seasonal variation of testosterone and waist to hip ratio in men: the Tromsø study.

Studies of seasonal variation in male testosterone levels show contradictory results. We report here a cross-sectional study of the seasonal variation in total and free testosterone, LH, and SHBG levels in 1548 men living in north Norway, a population exposed to a wide seasonal variation in temperature and daylight. Total testosterone showed a bimodal seasonal variation (P < 0.001) with a small peak in February, the nadir in June, and a more prominent peak in October and November. Free testosterone also showed a significant seasonal pattern (P < 0.001), with the peak in December and the nadir in August. These patterns persisted after adjusting for age and waist to hip ratio (P < 0.001). Lowest testosterone levels occurred in months with the highest temperatures and longest hours of daylight. Waist to hip ratio paralleled the change in daylight and temperature, with the highest values during the summer and was thus inversely related to the seasonal testosterone variation. The variations in hormone levels were large, with a 31% difference between the lowest and highest monthly mean level of free testosterone. Prospective studies are needed to establish the direction of the association and its etiology.

Adult↗

PubMed2006

Endoscopic procedures and diagnoses are not influenced by seasonal variations.

BACKGROUND: The occurrences of various GI diseases are thought to be influenced by seasonal variations. The present study was done to test the hypothesis that seasonal variations in endoscopic diagnoses reflect underlying patterns in the performance of endoscopic procedures. METHODS: The Clinical Outcomes Research Initiative (CORI) uses a computerized endoscopic report generator to collect endoscopic data from 73 diverse practice sites throughout the United States. We used the CORI database to analyze the date-specific occurrence of EGD and colonoscopy, as well as the endoscopic diagnoses of gastric ulcer, duodenal ulcer, and colorectal cancer. Time trends are analyzed by autocorrelation and by linear and nonlinear regression. RESULTS: Between January 2000 and December 2003, the number of EGDs and colonoscopies increased 2.5- and 4.1-fold, respectively. The rate of duodenal ulcer fell from 21.2 (15.6-27.5) to 19.0 (15.8-22.8) per 1000 EGDs. The rate of gastric ulcer fell from 42.6 (33.3-50.1) to 33.4 (29.5-38.7) per 1000 EGDs. The rate of colorectal cancer fell from 109.9 (98.3-122.8) to 72.2 (67.4-77.2) per 1000 colonoscopies. The time trends of neither endoscopic procedures nor endoscopic diagnoses revealed any seasonal variation or other cyclic pattern. CONCLUSIONS: The performance of endoscopic procedures is unaffected by any seasonal variation.

Endoscopy, Gastrointestinal↗

PubMed1991

Dimensional measurement of seasonal variation in mood and behavior.

Recent epidemiologic studies have found that the behaviors that characterize seasonal affective disorder (SAD) show seasonal variation in 92%-95% of the general population, suggesting that seasonal variation in behavior and mood is a continuous, dimensional variable extending throughout the general population, defined at the upper extreme by SAD. Research into population seasonality will require a dimensional measure of seasonal variation in mood and behavior that produces a broad, finely graded distribution of seasonality scores sensitive to individual differences throughout the entire range of scores. Accordingly, the Inventory of Seasonal Variation (ISV) was developed as such a measure. This study demonstrated that the ISV has high internal structural validity and is highly sensitive to individual differences in seasonality across its entire range of scores in the normal population. This latter characteristic is not shared by other existing measures of seasonality. Initial external validity of the ISV was supported in that the mean of ISV scores of a SAD sample was found to lie at the 97th percentile of the normal population of scores. Analysis of ISV scores revealed that a winter pattern of seasonality was reported by over 95% of subjects, a pattern that was more pronounced in women than men, while a summer type of seasonality was reported by only 0.6% of the general population.

Adult↗

PubMed1999

Statistical analysis of the seasonal variation in the twinning rate.

There have been few secular analyses of the seasonal variation in human twinning and the results are conflicting. One reason for this is that the seasonal pattern of twinning varies in different populations and at different periods. Another reason is that the statistical methods used are different. The changing pattern of seasonal variation in twinning rates and total maternities in Denmark was traced for three periods (1855-69, 1870-94, and 1937-84). Two alternative methods of analysis are considered. The method of Walter and Elwood and a trigonometric regression model give closely similar results. The seasonal distribution of twin maternities for the periods in the 19th century showed highly significant departures. For both twin and general maternities, the main peaks can be seen from March to June and a local peak in September. During the spring-summer season the twinning rates were higher than the total birth rates, indicating a stronger seasonal variation for the twin maternities than for the general maternities. For 1937-84, there was a similar, but less accentuated, pattern. Studies of other populations are compared with the Danish results. The more accentuated seasonal variation of twinning in the past indicate that some factors in the past affected women during summer-autumn and around Christmas time, making them more fecund and particularly to be more prone to polyovulation and/or more able to complete a gestation with multiple embryos.

Birth Rate↗

PubMed1994

Global patterns of seasonal variation in human fertility.

Pronounced and persistent seasonal patterns in fertility are observed in virtually all human populations. This paper presents evidence on these seasonal patterns. We note that the most pronounced seasonal patterns are in the southern United States, where births decline substantially in April and May, and in northern Europe, where births increase substantially in March and April. Although seasonal variations in fertility were more pronounced in earlier agricultural populations, we show that seasonality has increased in this century in some high income, low fertility populations such as Sweden. We use data on monthly temperature to analyze the potential role of temperature in explaining seasonal patterns. We find strong evidence that summer heat plays an important role in explaining the July-August trough in conceptions in the southern United States. We find little evidence, however, that temperature plays any role in explaining the pronounced June-July peak in conceptions in Sweden. Temperature also appears to be relatively unimportant in several other populations with substantial seasonal variations in births, suggesting that other factors play an important role in birth seasonality.

Birth Rate↗

PubMed1992

Seasonal variation of cerebral hemorrhage in 236 consecutive cases in Brussels.

BACKGROUND AND PURPOSE: Seasonal variation in the incidence of cerebral hemorrhage has been previously demonstrated. In this study, we sought to identify the climatological data best correlated with this seasonal variation. METHODS: In a retrospectively studied sequential series of 236 patients with nontraumatic cerebral hemorrhage observed in Brussels over a period of 8 years, we cumulatively grouped the dates of stroke occurrence into a single calendar year. RESULTS: We found marked seasonal variation in incidence, with the highest value (23%) observed in November-December and the lowest (10%) in July-August. Seasonal variations in incidence of cerebral hemorrhage were shown to be correlated not only with the inverse of ambient temperature, but also with the inverse of hours of sunshine and with ambient humidity. We found no difference between hypertensive and normotensive patients. CONCLUSIONS: Our study fails to bear out the hypothesis that the higher incidence of cerebral hemorrhage in late autumn and winter is due to the influence of low ambient temperature on blood pressure.

Adolescent↗