Ivar Heuch

Breast cancer risk by age at birth, time since birth and time intervals between births: exploring interaction effects

In a Norwegian, prospective study we investigated breast cancer risk in relation to age at, and time since, childbirth, and whether the timing of births modified the risk pattern after delivery. A total of 23 890 women of parity 5 or less were diagnosed with breast cancer during follow-up of 1.7 million women at ages 20–74 years. Results, based on Poisson regression analyses of person-years at risk, showed long-term protective effects of the first, as well as subsequent, pregnancies and that these were preceded by a short-term increase in risk. The magnitude and timing of this adverse effect differed somewhat by birth order, maternal age at delivery and birth spacing. No transient increase in risk was seen shortly after a first birth below age 25 years, but an early first birth did not prevent a transient increase in risk after subsequent births. In general, the magnitude of the adverse effect was strongest after pregnancies at age 30 years or older. A wide birth interval was also related to a more pronounced adverse effect. Increasing maternal age at the first and second childbirth was associated with an increase in risk in the long run, whereas no such long-term effect was seen with age at higher order births.

Use of alcohol, tobacco and coffee, and risk of pancreatic cancer.

Associations between pancreatic cancer and use of alcohol, tobacco and coffee were examined in a Norwegian prospective study of 16,713 individuals in which 63 cases occurred. The associations were assessed using techniques for stratified logistic regression. Of the potential risk factors considered, use of alcohol showed the strongest positive association, with an estimated relative risk of 5.4 for those with a frequent use as compared with non-drinkers (P less than 0.001). A clear positive association was also obtained with chewing of tobacco or use of snuff. For cigarette smoking a somewhat weaker association was observed. No association could be established for pipe smoking or coffee drinking. In general, more clear-cut results were found when analysis was restricted to histologically-verified cases.

Injury morbidity in an urban and a rural area in Tanzania: an epidemiological survey

BackgroundInjuries are becoming a major health problem in developing countries. Few population based studies have been carried out in African countries. We examined the pattern of nonfatal injuries and associated risk factors in an urban and rural setting of Tanzania.MethodsA population-based household survey was conducted in 2002. Participants were selected by cluster sampling. A total of 8,188 urban and 7,035 rural residents of all ages participated in the survey. All injuries reported among all household members in the year preceding the interview and resulting in one or more days of restricted activity were included in the analyis.ResultsA total of 206 (2.5%) and 303 (4.3%) persons reported to have been injured in the urban and rural area respectively. Although the overall incidence was higher in the rural area, the incidence of major injuries (≥ 30 disability days) was similar in both areas. Males were at a higher risk of having an injury than females. Rural residents were more likely to experience injuries due to falls (OR = 1.6; 95% CI = 1.1 – 2.3) and cuts (OR = 4.3; 95% CI = 3.0 – 6.2) but had a lower risk of transport injuries. The most common causes of injury in the urban area were transport injuries and falls. In the rural area, cuts and stabs, of which two thirds were related to agriculture, formed the most common cause. Age was an important risk factor for certain types of injuries. Poverty levels were not significantly associated with experiencing a nonfatal injury.ConclusionThe patterns of injury differ in urban and rural areas partly as a reflection of livelihoods and infrastructure. Rural residents are at a higher overall injury risk than urban residents. This may be important in the development of injury prevention strategies.

The impact of body mass index on the prevalence of low back pain: the HUNT study.

Study Design. A cross-sectional population-based study. Objective. To examine the association between body mass index and chronic low back pain, with adjustment for potential confounders. Summary of Background Data. Although many studies have investigated this association, it is still unclear whether there is a general relationship between body mass index and low back pain which applies to all populations. Methods. This study is based on data collected in the HUNT 2 study in the county of Nord-Trøndelag in Norway between 1995 and 1997. Among a total of 92,936 persons eligible for participation, 30,102 men and 33,866 women gave information on body mass index and indicated whether they suffered from chronic low back pain (69% participation rate). A total of 6293 men (20.9%) and 8923 women (26.3%) experienced chronic low back pain. Relations were assessed by logistic regression of low back pain with respect to body mass index and other variables. Results. In both sexes, a high body mass index was significantly associated with an increased prevalence of low back pain. In men the estimated OR per 5 kg/m2 increase in body mass index was 1.07 (95% CI: 1.03–1.12) and in women 1.17 (95% CI: 1.14–1.21), after adjustment for age, with a significantly stronger association in women. Additional adjustment for education, smoking status, leisure time physical activity, employment status, and activity at work hardly affected these associations. No interactions were found with most other factors. Conclusion. This large population-based study indicates that obesity is associated with a high prevalence of low back pain. Further studies are needed to determine if the association is causal.

Milk consumption and cancer incidence: a Norwegian prospective study.

Relationships between milk intake and cancer incidence were investigated after 11 1/2 years of follow-up of 15,914 individuals. A diagnosis of cancer was made in a total of 1,422 individuals. No association was established with total cancer incidence, in analyses adjusted for sex, age and residential characteristics. However, a strong positive association with milk consumption was observed for cancers of the lymphatic organs (odds ratio 3.4 for greater than or equal to 2 glasses per day vs less than 1; 95% confidence interval 1.4-8.2). An inverse association was found for cancer of the bladder. Kidney cancer and cancers of the female reproductive organs (except the uterine cervix) showed weak positive associations with milk intake.

The short-term and long-term effect of a pregnancy on breast cancer risk : a prospective study of 802 457 parous Norwegian women

Time-related effects of a pregnancy on breast cancer risk were examined in a population-based prospective study of 802,457 parous Norwegian women aged 20-56 years. The mean follow-up time was 16.4 years. A total of 4787 women were diagnosed with breast cancer. We observed a short-term increase in risk of breast cancer after a full-term pregnancy, with a maximum 3-4 years after delivery, followed by a long-lasting decrease in risk. The maximum risk was about twice the risk for women whose last delivery was 20 or more years previously (incidence rate ratio = 1.99, 95% confidence interval = 1.70-2.33). Compared with nulliparous women, those with one or two children were at higher risk in the first decade after the last pregnancy, whereas those with three or more children were at lower risk in most categories of time since the last birth. The positive association between breast cancer risk and age at last birth was markedly reduced after adjustment for time since last birth. We conclude that there is a non-linear relationship between breast cancer incidence and time since last birth. Part of the relation with age at last birth may be attributed to the association with time since last birth.

Does age at natural menopause affect mortality from ischemic heart disease

We examined the relationship between age at natural menopause and mortality of ischemic heart disease in 19,309 Norwegian postmenopausal women. A total of 2767 fatal infarctions occurred during 29 years of follow up. Overall, a relatively weak inverse relationship was seen with approximately 10% lower ischemic heart disease mortality in women aged > or = 47 years at the menopause compared to women with an early menopause (< 44 years). Risk estimates were similar for women aged 47 and more at menopause. However, the inverse relationship was stronger and statistically significant (p = 0.01) in women aged less than 70 years. In this group of women, we observed a nearly 60% reduction in the ischemic heart disease mortality in women with a late menopause (> or = 53 years) compared to women aged < 44 years at menopause (mortality rate ratio = 0.42; 95% confidence interval 0.25-0.72). This protective effect of a late menopause is reduced with advancing age, however, and is of minor significance in the age groups where the great proportion of the ischemic heart disease deaths occur.

Menstrual factors and breast cancer risk

Relationships between menstrual factors and breast cancer risk were investigated in a prospective study of 63,090 Norwegian women. A total of 1565 cases of breast cancer occurred during follow‐up from 1961 through 1980. The risk of breast cancer decreased with increasing age at menarche (P = 0.06) and increased with increasing age at menopause (P = 0.005) in analyses adjusted for age, urban/rural place of residence, parity, and age at first and last birth. The results correspond to an average increase in breast cancer risk of 4.0% for each year of decrease in age at menarche, and an increase in risk of 3.6% for each year of increase in age at menopause. The protective effect of early menopause was strongest for breast cancer diagnosed in patients 80 years of age or older. No clear relationship was seen between menstrual irregularities and breast cancer risk.

Lactation and cancer risk: is there a relation specific to breast cancer?

Relations between previous lactation experience and risks of cancer of the breast and other sites were investigated after follow-up of 50,274 parous women from 1961 through 1980. Among women with complete information on lactation, 5102 developed cancer and, of these, 1136 were diagnosed with breast cancer. Analyses of associations with mean duration of lactation per birth and duration for each of the three first births suggested a nonlinear relation to breast cancer. The highest risk was observed for those with intermediate duration of breast feeding, whereas lower risks were found among those with very short or very long duration. For all nongenital cancers combined, decreased risks were observed among those with the longest duration of breast feeding. However, among cancers of specific sites, a significant inverse association was found for pancreatic cancer only. The overall impression given by our data is that breast feeding is not strongly related to risks of breast cancer or any other common cancer.

Equilibrium populations of heterostylous plants

Abstract A general relation is derived which must be satisfied by the equilibrium frequencies of the incompatibility types occurring in populations of heterostylous plants. Specific assumptions are made about the underlying genetic mechanism, but these are fulfilled in practically all relevant cases. With usual mating systems corresponding to pollen or zygote elimination and no fitness differences, it follows that all incompatibility types must be equally frequent. Given different fitness values, the general relation leads to more complex equations determining the frequencies. These equations are used for estimating fitness values of the Long, Mid and Short types in Lythrum salicaria . Expressions for the equilibrium frequencies are also found for a special mating system in Oxalis alpina .