Time trend and age-period-cohort effects on gastric cancer incidence in Zaragoza and Navarre, Spain.

STUDY OBJECTIVE: To describe time trends in gastric cancer incidence in Zaragoza and Navarre, and to investigate time period and birth cohort as determinants of such trends. DESIGN: Cases from two registries were grouped into five year intervals and the following were calculated: age specific and sex specific incidence rates, and the male to female ratio. Log linear models including age, period of diagnosis, and birth cohort were fitted. SETTING: The Zaragoza Cancer Registry covers the province of Zaragoza, which has a population of 824,776 (403,755 men and 421,021 women). The Navarre Cancer Registry covers the province of Navarre which has 512,512 inhabitants (254,786 men and 257,726 women). In both cases population figures were based on the late census. PATIENTS: These comprised incident cases of gastric cancer reported to the Zaragoza Cancer Registry in 1963-87 and to the Navarre Cancer Registry in 1973-87. MAIN RESULTS: Navarre registered higher adjusted and cumulative rates than Zaragoza for both sexes. In both provinces, there were relative declines in the rates for men and women of 3% and 4% respectively per year. In Zaragoza, the risk of developing stomach cancer fell in generations born between 1888 and 1933, and rose in subsequent birth cohorts in both sexes, while in Navarre the cohort effect showed an approximately linear risk for both sexes. Both provinces recorded increases in risk associated with cohorts born between 1933 and 1943. CONCLUSION: The incidence rates of gastric cancer fell in both Zaragoza and Navarre. The reason for the greater incidence of gastric cancer in Navarre remains unknown. Trends in rates seem to be mainly linked to birth cohort. Increases in risk in generations born after 1933 may be ascribable to nutritional deficiencies in the early years of life.     

AIDS trends among Hispanics in the United States.

OBJECTIVES. In 1991 the incidence of acquired immunodeficiency syndrome (AIDS) in the United States was 31.6 per 100,000 population among Hispanics and 11.8 per 100,000 among non-Hispanic Whites. The purpose of this study was to further describe the AIDS epidemic among Hispanics by examining differences in risk factors among different Hispanic groups (as defined by birthplace). METHODS. AIDS cases reported to the Centers for Disease Control and Prevention from 1988 through 1991 were reviewed. RESULTS. For men, except for those born in Puerto Rico, the predominant exposure category was male-male sex. The proportion of cases due to injection drug use was 35% among Hispanic men born in the United States, 27% among men born in the Dominican Republic, and 61% among men born in Puerto Rico, but < 10% among other Hispanic men and non-Hispanic White men. For women the predominant exposure category was injection drug use among Hispanics born in the United States (56%) and Puerto Rico (46%) and among non-Hispanic Whites (42%). The proportion of cases associated with injection drug use was significantly lower (< 30%) among other Hispanic women. CONCLUSIONS. AIDS prevention strategies must be geared toward different exposure categories among different Hispanic groups.     

An age-period-cohort analysis of 50,875 AIDS cases among injecting drug users in Europe

BACKGROUND: The long average incubation time from HIV infection to AIDS makes it difficult to estimate recent HIV transmission from AIDS incidence data. Age-period-cohort (APC) analysis can separate out the effects of age, calendar time and birth cohort to provide a clearer picture of transmission trends. METHODS: AIDS incidence data from 1981 to 1994 among intravenous drug users (IDU) for 12 Western European countries were used. Yearly incidences per 100,000 population or 100,000 person-years were calculated by age at diagnosis and 5-year birth cohort (1950-1954, 1955-1959, 1960-1964, 1965-1969 and 1970-1974), and corrected for reporting delay. Incidence patterns were compared between birth cohorts and countries. RESULTS: For most countries the impact was greatest on the cohort born 1960-1964. Comparing incidence patterns in the 1965-1969 to 1960-1964 cohorts suggest the epidemic has plateaued at low to intermediate levels in Austria, Greece and the North-Western European countries, and at high levels in France, Italy and Switzerland. For most countries transmission amongst the 1970-1974 as compared to the 1965-1969 cohorts could not be assessed due to small numbers and short follow-up time. In Spain the epidemic was uncontrolled with a high incidence among recent birth cohorts. In Portugal the epidemic was still at an early and expanding phase. CONCLUSIONS: The APC analysis revealed large country differences in the dynamics of the HIV/AIDS epidemic among IDU. Full interpretation of these differences is dependent on information from other sources about the local public health response and trends in drug injecting behaviours. Earlier introduction of the virus and higher prevalence of injecting drug use may explain some of the generally higher incidence in Southern European countries, but the larger part of it is most likely explained by local characteristics of drug users, such as younger age and more frequent sharing of needles and syringes, and a less effective public health response.     

Drug-related mortality in Denmark 1970-93

We analysed drug-related mortality in Denmark with respect to secular trends, gender, and regional variations, for the period 1970-93, for all deaths from poisoning and among drug addicts. The study was based on the Register of Causes of Death in Denmark and included 6,229 drug-related deaths, defined by specific combinations of manner of death, underlying cause of death, and contributory cause of death. The main outcome measure is age-specific mortality rate. A total of 63% of the drug-related deaths were registered as unnatural deaths. During the period studied, mortality increased for men in the 25 49 year age group and for women in all age groups over 25 years of age. For both men and women, the youngest birth cohorts from the mid-1950s and 1960s suffered much higher mortality than those born before 1950; however, the three youngest birth cohorts had almost the same mortality. During the entire period, mortality in the capital, Copenhagen, was much higher than in the provinces, but in the last years, a more favourable trend has been seen in Copenhagen.     

High coronary heart disease rates among Dutch women of the baby boom, born 1945-1959: age-cohort analysis and projection

BACKGROUND: After a steep decline in older generations, coronary heart disease mortality is stagnating in female cohorts born after the Second World War. We analysed past trends and predicted future health care needs for coronary heart disease in the Dutch population. METHODS: A loglinear age-cohort model relates numbers of deaths and hospital admissions for coronary heart disease to sex, age, birth cohort and population size, and projects age-cohort changes over the future population. Population size, population forecasts and coronary heart disease mortality (period 1970-1999) are from vital statistics. Numbers of hospitalised acute coronary events are from the nationwide hospital register (period 1980-1999). RESULTS: Among men, the rate ratios of deaths and hospital admissions were, respectively, 0.21 (death) and 0.78 (survivors at discharge) in the cohorts born in the period 1948-1962 compared to the period 1918-1922. Among women, the same rate ratios were 0.41 and 1.89. The projection model predicts 22% less deaths from coronary heart disease and 22% more survivors of an infarction in 2015, among men. Among women, there will be 5% less deaths and 70% more survivors of an infarction, most of these being middle age members of the baby boom cohorts. CONCLUSIONS: Stagnating all-cause mortality is correlated with an upward trend in coronary heart disease risk in the female baby boomers. Heart health care needs among middle-aged women will increase sharply. These changes are correlated to high lung cancer mortality and high smoking rates in these cohorts.     

Cohort trends in the age of initiation of drug use in Australia

AIM: To examine birth cohort trends in the prevalence of use and the age of initiation of use of: alcohol, tobacco, cannabis, amphetamines, LSD, and heroin. METHOD: Data were taken from the 1998 National Drug Strategy Household Survey, a survey of a representative sample of Australians aged 14 years and over. Nine five-year cohorts were examined among persons born between 1940 and 1984. The weighted prevalence of use by ages 15 years, 21 years, and lifetime use, was estimated, as was the average age of first use among users. The significance of trends was tested using logistic regression (for lifetime use, use by 15 and 21 years) and linear regression (for age of first use). RESULTS: Lifetime prevalence of alcohol and tobacco use was similar among all birth cohorts. The prevalence of illicit drug use--cannabis, amphetamines, LSD and heroin--increased with successive birth cohorts and more recent birth cohorts reported using licit and illicit drugs at a younger age. CONCLUSIONS: More recent cohorts are more likely to use illicit drugs at some point in their lives. Greater numbers of persons from more recent birth cohorts may be at risk of developing substance-related problems.     

Variations in the risk of disability pension in Norway 1970-99. A gender-specific age-period-cohort analysis

AIMS: A study was undertaken to investigate whether cohort or period effects could explain the varying and generally increasing incidence of disability pension in Norway between 1970 and 1999. METHODS: The study used data from a complete national register of new disability cases in Norway, including all cases of disability pension in the 16-60 age group categorized according to age and gender for each year from 1970 to 1999. The population at risk was defined for each year from census data and number of individuals already receiving disability pension. Data were organized in five-year age groups, five-year time periods and corresponding overlapping nine-year birth cohorts. Age- and gender-specific rates were displayed graphically for periods and cohorts. Separate Poisson regression models were fitted for age periods and age cohorts. Finally a combined age, period, and cohort model was applied. RESULTS: The overall incidence was 7.4/1,000 non-disabled persons per year for women and 6.0/1,000 for men. For women 52.1% of the cases were in the 51-60 age group, whereas the corresponding figure for men was 57.6%. Statistical analysis showed an increasing trend for both genders, more pronounced for women than men. All time periods deviated significantly from the trend, either upwards or downwards. Age-cohort models showed less variation, but recent cohorts had higher than expected rates, especially for men. CONCLUSIONS: Further studies should investigate why Norwegian women were more affected by the period effects than men. An increasing incidence of disability pension among recent cohorts is a major challenge for the Norwegian welfare system.     

Effect of birth cohort on risk of hip fracture: age-specific incidence rates in the Framingham Study

OBJECTIVES: This study examined the effect of birth cohort on incidence rates of hip fracture among women and men in the Framingham Study. METHODS: Age-specific incidence rates of first hip fracture were presented according to tertile of year of birth for 5209 participants of the Framingham Study, a population-based cohort followed since 1948. Sex-specific incidence rate ratios were calculated by Cox regression to assess the relation between birth cohort and hip fracture incidence. RESULTS: An increasing trend in hip fracture incidence rates was observed with year of birth for women (trend, P =.05) and men (trend, P =.03). Relative to those born from 1887 to 1900 (incidence rate ratio [IRR] = 1.0), age-specific incidence rates were greatest in the most recent birth cohort, born from 1911 to 1921 (IRR = 1.4 for women, IRR = 2.0 for men), and intermediate in those born from 1901 to 1910 (IRR = 1.2 for women, IRR = 1.5 for men). CONCLUSIONS: Results suggest risk of hip fracture is increasing for successive birth cohorts. Projections that fail to account for the increase in rates associated with birth cohort underestimate the future public health impact of hip fracture in the United States.     

Declining rates of hepatocellular carcinoma in urban Shanghai: incidence trends in 1976–2005

In China, hepatocellular carcinoma (HCC) incidence rates in several registry catchment populations are amongst the highest worldwide. The incidence rates in urban Shanghai were analyzed between 1976 and 2005 to describe and interpret the time trends. Age-specific and age-standardized rates were calculated and graphically presented. An age-period-cohort model was fitted to assess the effects of age at diagnosis, calendar period, and birth cohort on the changing HCC incidence rates. In total, 35,241 and 13,931 men and women were diagnosed with HCC during 1976–2005 in urban Shanghai. The age-standardized incidence rates in urban Shanghai were 33.9 per 10⁵ among men and 11.4 per 10⁵ among women in 1976–1980, but decreased in both sexes to 25.8 per 10⁵ and 8.5 per 10⁵, respectively by 2001–2005. Accelerating rates in birth cohorts born in the early-1930s and decelerating rates circa 1945 were observed in both sexes, with further accelerations noted in the late-1950s (in women) and early-1960s (in men). Given the parameterization, increases in risk of HCC were seen in successive male and female generations between 1900 and 1935, followed by a further increase among successive cohorts born around 1960, with a reduction in risk in the most recent generations. The incidence rates of HCC in urban Shanghai from 1976 to 2005 have declined in both sexes, with the complex but similar patterns observed in successive generations suggestive of a shared changing prevalence in risk factors in men and women, with a role possibly for HBV interventions reducing risk of HCC in cohorts born after 1960.     

Trends in reproductive, smoking, and other chronic disease risk factors by birth cohort in a large occupational study

PURPOSE: To illustrate the value of using large cohort studies to identify birth cohort trends in several chronic disease risk factors.METHODS: In collaboration with the American Registry of Radiologic Technologists (ARRT) and the University of Minnesota, the National Cancer Institute (NCI) initiated a cohort study of radiologic technologists who were certified by ARRT for at least two years between 1926 and 1982. Over 90,000 technologists (nearly four-fifths female) from all 50 states responded to a mailed questionnaire on reproductive, medical, work, and lifestyle factors. Ten, mostly five-year, birth cohorts, from before 1920 through 1960 and later, were evaluated.RESULTS: In this population, the mean height of both men and women generally rose in each subsequent birth cohort. The proportion of men who smoked before age 18 fell among those born since the late 1920s. In contrast, the proportion of women smoking before age 18 rose among those born since the early 1950s, reaching 14.2% among those born in 1960 and later. The mean age at menarche fell, until leveling off at 12.5, among those born after 1940. Recent birth cohorts (since 1950) show among the highest mean ages at birth of first child (>26 yeras), highest rates of nulliparity at age 25 (>/=63%), and lowest mean parity levels (相似文献   

Age, period and cohort effects on the risk of major depression: results from five United States communities

Rates of major depression are presented from the recently completed Epidemiologic Catchment Area (ECA) Study based on probability samples of over 18,000 adults, 18 years of age and older, living in five U.S. communities. These rates were analyzed to describe simultaneously the changes affecting successive birth cohorts and the changes associated with the period in which the onset of the disorder occurred, using age-period-cohort (APC) models. The non-identifiability problem inherent in all APC models was resolved by assuming that the linear period effect and linear cohort effect were non-negative. This assumption is consistent with our a priori substantive knowledge of the disease. Under this assumption, as the linear period effect varies from its minimum to its maximum values, a family of curves representing the possible effects of a factor was generated for each of the time factors--age, period and cohort. The results of the analysis showed a sharp increase in rates of major depression among both men and women in the birth cohort born during the years 1935-1945. The rates among females, however, seemed to have stabilized in the generations born since 1945, while the rates in males continued to rise sharply among the cohorts born in the following decade, after which, in 1955, they also levelled off. In contrast, the rates associated with period of onset of major depression continued to increase between the years 1960-1980 among both men and women of all ages studied. These findings are considered in light of the persistent concentration of depression in women and in biologically related members of families of affected individuals.     

Trends in smoking by birth cohorts born between 1900 and 1977 in Japan

BACKGROUND: The present study aimed to elucidate the changing patterns of smoking among successive birth cohorts in Japan. METHODS: Birth-cohort-specific smoking prevalence was estimated for birth cohorts born from 1900 to 1952, using data pooled from four prospective studies (242,330 men and 274,075 women), and for birth cohorts born from 1925 to 1977, using National Nutrition Survey data. RESULTS: For men, two peaks were observed in smoking prevalence, in the 1925 and late-1950s birth cohorts, while a trough was observed for the 1938 birth cohort. For women, ever smoking prevalence was lowest among the 1930s birth cohorts. After the female 1940s birth cohorts, no peak was observed until the end of our observations, the 1970s birth cohorts. Although Japanese women have historically tended to start smoking at later ages, recently, smoking habits have widely expanded among females in young birth cohorts. CONCLUSIONS: Smoking trends in Japanese men and women vary by birth cohorts. Smoking cessation should continue to be strongly promoted among men, although the younger generation has widely adopted a nonsmoking lifestyle. For women, efforts for preventing the onset of smoking, while necessary among the younger generation, should even be enhanced among middle-aged women.     

Twenty-five years of the AIDS epidemic in Brazil: principal epidemiological findings, 1980-2005

The Brazilian AIDS epidemic is undergoing important changes in its third decade. The present article reviews some central findings: the proportional reduction in cases related to injection drug use; the stability, in recent years, of new cases in the male homosexual/bisexual population; and the relative and absolute increment in heterosexual transmission, even though the estimates of incident rates still point to the first two categories mentioned as those most affected by the epidemic. Still should be detached the persistent increase in incidence rates among women and its stability in the younger age groups, probably the result of behavior changes (such as the consistent use among youth of condoms in sexual relations with casual partners and a reduction in cases related to injection drug use). It is well-know that HIV prevalence in the general population has stabilized at less than 1%, which characterizes Brazil as one of the countries with a concentrated epidemic. The article also emphasizes the growth of AIDS morbidity-mortality in the less favored socioeconomic strata and in women, and the stability of the mortality rate among men.     

Age, period and birth-cohort effects on marriage rates in Japanese women between 1985 and 2005, and comparison of trends of effects between marriage and birth rates

OBJECTIVE: An age-period-cohort (APC) analysis was performed to provide information about age-, period-, and cohort-specific effects on marriage trends in Japanese women. In addition, the relationships of the trends of age-, period-, and cohort-specific effects between marriage and birth were analyzed. METHODS: We obtained data regarding marriages of Japanese women aged between 19 and 38 years for the period of 1985 to 2005 from the National Vital Statistics. Population data used were for an estimated population, obtained from the Population Estimates Annual Reports. Standard cohort tables comprising marriage and population data were analyzed using a Bayesian APC model to identify age-, period-, and cohort-specific effects on marriage rate trends. Previously obtained data for a similar APC-analysis of birth trends were used to compare the trends in the effects of age, period, and cohort on marriage and birth patterns. For this purpose, the estimated values for each effect were normalized. RESULTS: With regard to the marriage trends in Japanese women, the effect of age was the greatest, peaking at the age of 25 years. The period effect increased after 1997; however, its effect was relatively limited as compared to the other effects. The cohort effect, which was greater than the period effect and less than the age effect, on marriage trends showed a decreasing slope for birth cohorts born after 1966 and subsequent increase after 1982. Comparison of age, period and cohort effects between the trends in marriage and birth rates showed that the age effect distinctly peaked at 25 and 28 years for marriage and births, respectively. The period effect on marriage and birth showed a decreasing trend until 1991 and subsequent increased in 1992 and 1997 for births and marriage, respectively. With regard to the cohort effect on birth rates, a decreasing trend was observed for the birth cohorts after 1961, with increase after 1977. However, with regard to the cohort effect on marriage rates, the decreasing trend observed for birth cohorts after 1966 showed an increase after 1982. CONCLUSION: Among age, period, and birth cohort, age is the most influential factor affecting marriage rates. Period effects appear relatively small, but they increased after 1997. Cohort effects reduced for birth cohorts born after 1966 and subsequently increased after 1982. Results of the comparison study showed that changing patterns of age, period and cohort effects had very similar influences on the trends for marriage and birth rates. However, a 3-year difference was observed between the peaks of the age effect on the two rates. A time lag of 5 years was observed between the turning point in the trend of period effects for marriage and birth rates. The changing patterns of cohort effects on marriage and birth rates were similar, but the turning point for the marriage pattern occurred in a 5-year younger cohort compared with the birth pattern.     

An analysis by birth cohort of alcohol consumption by adults in Great Britain 1978-1998

AIMS AND METHODS: The General Household Survey for Great Britain has, since 1978, in even numbered years, included questions on alcohol consumption. A cohort analysis was applied to these sequential cross-sectional data. RESULTS AND CONCLUSIONS: Analysis confirms that, after about age 20 years, both men and women, as they grow older, become more likely to be non- or very light drinkers. Men are also less likely to be heavy drinkers as they grow older, but for women the picture is less clear-cut. Cohort effects can also be discerned, but are much less obvious than for smoking. There is a general trend for members of later cohorts at any age to be less likely to be non- or very light drinkers and more likely to be heavy drinkers, than members of earlier cohorts. However, for men, this trend seems to have ended with those born from about 1927 to 1931, while for women the trend has continued and possibly become stronger in cohorts born after 1927-1931.     

First Anal Intercourse and Condom Use Among Men Who Have Sex with Men in Switzerland

The aim of this study was to analyze the circumstances of first anal intercourse (FAI) among men who have sex with men (MSM) and to identify factors associated with condom use at this event. We conducted a cross-sectional survey among a convenience sample of MSM living in Switzerland (N = 2,200). Anonymous questionnaires were distributed using Swiss gay communication channels (newspapers, associations, websites) and gay bathhouses. We gathered data on age at FAI, age of the partner, degree of familiarity with him, place of first meeting, and sociodemographic indicators. We did not ask whether FAI was insertive, receptive, or both. Data were stratified by birth year classes (birth cohorts). The median age at FAI fell from 24.5 years among men born before 1965 to 20.0 years among those born between 1975 and 1984 (p < .001). In each birth cohort, between 20 and 30% reported a partner 10 years older or more. Of eight variables examined in multivariate analysis, two were positively associated with condom use: age of participants at FAI and low degree of familiarity between partners. Conversely, large age discrepancy between partners was negatively associated with condom use. In conclusion, our data showed that early initiation of anal intercourse and large age discrepancy were associated with risk taking: a pattern of initiation that may facilitate HIV transmission from older to younger cohorts of MSM. Since age at FAI is on the decrease, there is an urgent need to heighten awareness of prevention actions regarding sexual debut of MSM.     

Incidence rates of malignant mesothelioma in Denmark and predicted future number of cases among men

OBJECTIVES: This study analyzed the incidence rates of malignant mesothelioma in Denmark in order to predict the future number of cases that will occur among Danish men. METHODS: The 1912 cases of malignant mesothelioma reported to the Danish Cancer registry in 1943-1993 were analyzed in order to describe current incidence rates. By a Poisson regression model the relative risks of synthetic birth cohorts were estimated and used in the prediction of the future number of cases that will occur among Danish men. RESULTS: The incidence rate increased to 1.33 per 100000 person-years in 1983-1987 among men and to 0.51 in 1973-1977 among women. From the Poisson regression model, the risk for birth cohorts of men, relative to the 1940-1944 cohort, peaked in the 1940-1944 cohort and decreased to 0.57 in the 1950-1954 cohort. The age-specific incidence rate peaked at 246 per 100000 person-years in the age group 80-84 years. The future annual number of mesothelioma cases is expected to peak around 2015 with 93 cases among men born before 1955. CONCLUSIONS: The fit of the models was not ideal, but with careful interpretation of the results, it was concluded that a further increase in the number of mesothelioma cases can be expected, and the effect of regulating the environmental exposure to asbestos cannot be expected within the next 10-15 years.     

Thirty-year trends of physical activity in relation to age, calendar time and birth cohort in Finnish adults

BACKGROUND: The aim of this article was to investigate time trends 1972-2002 in leisure time, occupational and commuting physical activity across birth cohorts in Finnish adults. METHODS: The study population comprised 59 028 men and women aged 25-64 years who participated in the FINRISK Study. The first birth cohort was born in 1913 and the last in 1977. Prevalence of physical activity was reported across birth cohorts and study years and change in the prevalence was tested using log-linear regression analysis. RESULTS: The prevalence of leisure-time physical activity increased between 1972 and 2002 from 66% to 77% in men and from 49% to 76% in women. In each study year, the younger people were more active than the older ones. However, within the birth cohorts, physical activity tended to increase with age. The prevalence of physically demanding work decreased from 60% to 38% in men and from 47% to 25% in women and the prevalence of daily commuting activity decreased from 30% to 10% in men and from 34% to 22% in women, in the same time period. In the 1970s and the 80s, the older people had more physically demanding work than the younger ones, but within the birth cohorts, occupational activity decreased with age. CONCLUSION: During the past 30 years, the prevalence of leisure-time physical activity has increased, while the prevalence of occupational and commuting physical activity has decreased. The cross-sectional association of age with different types of physical activity was different from that assessed within the birth cohorts.     

Trends in the incidence of cancer of the corpus uteri in Denmark, 1943-1980

The occurrence of cancer of the corpus uteri in Denmark is examined by the use of data from the Danish Cancer Registry. The study population consists of 14,149 cases diagnosed with cancer of the corpus uteri between 1943 and 1980. Since 1943, the incidence has been steadily increasing. The trend in the incidence rates varies in different age groups, and examination of birth cohorts shows higher rates after the age of 50 for more recent generations. The trend is evaluated in relationship to changes in diagnostic practices and to changes in prevalence of risk factors. Of the latter, estrogen use is considered a plausible explanation for the increasing incidence in women aged 55-64 years Correction of the age-specific incidence rates for hysterectomy reveals a pattern very similar to that of breast cancer.     

Trends in reproductive,smoking, and other chronic disease risk factors by birth cohort and race in a large occupational study population

PURPOSE: To illustrate the value of cohort studies to assess trends in chronic disease risk factors. METHODS: In collaboration with the American Registry of Radiologic Technologists and the University of Minnesota, the National Cancer Institute initiated a cohort study of cancer among radiologic technologists. More than 90,000 technologists who responded to a mailed questionnaire were grouped into ten birth cohorts from before 1920 through 1960 and later, and stratified by self-reported racial/ethnic groups. Trends in height, smoking, and reproductive factors were analyzed. RESULTS: Among the trends observed were that the proportion of young men (< 18 years) smoking generally fell in each birth cohort after 1925, whereas the proportion of young women smoking rose for those born after 1950. Among women born since 1940, the mean age at menarche for white women has remained at 12.5 years, but has declined among black and Asian/Pacific Islander women. Recent birth cohorts (since 1955) show among the highest mean ages at birth of first child (> 26 years), highest rates of nulliparity at age 25 (>/= 63 %), and lowest mean parity levels (< or = 1.7) compared with earlier cohorts. CONCLUSION: Analyses of large cohorts can clarify birth cohort trends in chronic disease risk factors.