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I Heuch

Publications and source records attributed to I Heuch.

At least 19 recordsLinked to original sources
PubMed2001

Attributable fractions: fundamental concepts and their visualization.

A general methodology for visualizing attributable fractions in epidemiology is described. The methodology applies to the multifactorial exposure situation and embraces various types of attributable fractions including adjusted, sequential and average attributable fractions. The concept of the scaled Venn diagram plays a central role, illustrating total disease risk and excess disease risk attributable to the exposures as areas in a unit square. This forms the ground for making simple pie charts of attributable fractions summing to 1 (or 100%). The potential applications extend from cohort and cross-sectional data to data from case-control studies. The methodology is illustrated by theoretical as well as empirical examples including the risk of motor fatalities attributable to driver's blood alcohol concentration and age, and the prevalence of chronic cough attributable to smoking habits, occupational exposure to dust or gas, and residence. A total of 40 figures illustrate the methodology.

Algorithms↗
PubMed2000

Menstrual and reproductive factors and risk of gastric cancer: a Norwegian cohort study.

OBJECTIVE: To explore relations between menstrual and reproductive factors and incidence of gastric cancer in a cohort study of 63,090 Norwegian women, followed over a period of 29 years. METHODS: Associations with potential risk factors were evaluated by Poisson regression analysis, considering 572 cases of gastric cancer diagnosed in women aged less than 80 years. RESULTS: Age at menarche showed a moderate inverse association with overall risk of gastric cancer (incidence rate ratio 0.93 per year; 95% confidence interval 0.88-1.00). No association could be established with age at menopause. Among women aged less than 50 years, an old age at first delivery was related to an increased risk, mainly of cancer of the distal part of the stomach. In multiparous women aged 50 years or more, relations with childbearing history differed significantly between subsites. Women with many pregnancies over a short period of time had an increased risk of cancer of the proximal part of the stomach. In the distal part, pregnancies over a long period seemed to confer a higher risk. CONCLUSIONS: Relations between reproductive factors and risk of gastric cancer should be assessed separately for pre- and postmenopausal women and for subsites.

Abortion, Induced↗
PubMed1999

Joint effects on cancer risk of age at childbirth, time since birth and attained age: circumventing the problem of collinearity.

In previous studies of female cancer risk, we introduced a new method for circumventing the problem of collinearity in age-adjusted analysis of the joint effects of age at birth and time since birth. The basic idea was to estimate the pure age effect considering nulliparous women, assuming that the age effect is common to all women. However, risk estimates for attained age obtained in this manner may suffer from bias, in particular in small data sets, which may in turn influence risk estimates for reproductive factors among parous women. Certain factors possibly affecting cancer risk among nulliparous women only, for instance biological infertility, might also introduce bias. The purpose of this paper is to investigate the accuracy of risk estimates obtained by the joint approach, and to reveal the extent of bias in traditional separate age-adjusted analyses of age at birth or time since birth among parous women. Results are based on analyses of simulated data sets reflecting reproductive and demographic characteristics of a cohort of 1.1 million Norwegian women. Incidence rate ratios are calculated in Poisson regression analyses of person-years at risk. Our simulations show that the joint analysis in general yields unbiased risk estimates, but the number of cases must be rather high to achieve reliable results. Risk estimates from separate analyses can be seriously biased, although the amount of bias depends on the strength and direction of associations with cancer risk. With a total of 5500 cancer cases, the estimators for age at last birth and time since last birth were 13-78 per cent and 5-66 per cent more efficient in the joint than in the separate analysis, respectively. Significance levels were close to the nominal 5 per cent in the joint analysis, but about twice as high in the separate analysis. Adding an effect of biological infertility on cancer risk among nulliparous women, without taking it into account in the analyses, did not seriously affect risk estimates in the joint model.

Adult↗
PubMed1999

Modeling effects of age at and time since delivery on subsequent risk of cancer.

We describe a simple model for examining the temporal effects of childbirth on cancer risk, considering data on uniparous and nulliparous women, from either a cohort or case-control study design. For uniparous women, the expression for risk includes terms for age at delivery and time since delivery. With a suitable definition of the effect of uniparity, no terms relating to delivery are needed for nulliparous women. If the pure age effect is assumed to be the same in all women, the effects of age at delivery and time since delivery are both estimable, despite the linear dependence involving attained age in uniparous women. Omitting terms for time since delivery and considering the heterogeneity of age-specific effects of uniparity provides a valid test for the effect of time since delivery, although risk estimates are biased. Tests based on linear interaction terms for age at delivery and attained age, as applied in recent case-control studies, are not appropriate for investigating the effect of time since delivery. We show how our basic model may be applied to the analysis of case-control data from a Norwegian study of breast cancer. We then compare these results with those from other models.

Age Factors↗
PubMed1998

Risk of primary childhood brain tumors related to birth characteristics: a Norwegian prospective study.

Relations between birth characteristics and risk of primary brain tumor were explored in a prospective study of the 1,489,297 children born in Norway between 1967 and 1992. A total of 459 primary brain tumors, including 78 medulloblastomas and 168 astrocytomas, were diagnosed in the age interval 0-15 years. The overall risk of brain tumor depended on the season of birth (p = 0.01), with a higher risk for children born in winter than those born in spring [incidence rate ratio (IRR) = 1.52; 95% confidence interval (CI) 1.18-1.97]. An inverse association was observed with father's age at birth of child. The risk of medulloblastoma was positively associated with birth weight (IRR = 1.27/500 g; p = 0.05). Inverse relationships with length at birth were found for astrocytoma in the 0-1 and 5-10 year age intervals. Among 5-10-year-old children, birth weight was also inversely related to risk of astrocytoma. Our results suggest that risk factors may differ over age intervals and histological subgroups.

Adolescent↗
PubMed1998

Reproductive factors and fatal hip fractures. A Norwegian prospective study of 63,000 women.

STUDY OBJECTIVE: The aim of the study was to investigate the impact of reproductive variables (age at menarche, menopause, first and last birth as well as parity, lactation, and abortions) on hip fracture mortality. DESIGN AND SETTING: A prospective study in Norway with more than 60,000 women followed up for 29 years. A total of 465 deaths as a result of hip fracture were recorded. MAIN RESULTS: Statistically significant linear relations (p < or = 0.02) were found between both age at menarche and length of reproductive period (defined as age at menopause to age at menarche) and the mortality of hip fractures in women aged less than 80. The death rate for women with a late menarche (> or = 17 years) was twice that of the women with relatively early menarche (< or = 13 years). Compared with women with less than 30 years between menopause and menarche, the mortality rate ratio in women with more than 38 reproductive years was 0.5. We also found an inverse relation with age at first birth. CONCLUSIONS: This study supports by hypothesis that an early menarche and a long reproductive period protect against hip fracture mortality. High age at first birth may also be protective.

Abortion, Spontaneous↗
PubMed1997

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.

Age Factors↗
PubMed1996

Reproductive factors and incidence of epithelial ovarian cancer: a Norwegian prospective study.

To examine relations between the risk of epithelial ovarian cancer and time-related effects of pregnancies, we analyzed data from a prospective study of 1,145,076 women in Norway aged 20 to 56 years. The mean follow-up time per woman was 16.4 years and a total of 1,694 women were diagnosed with epithelial ovarian cancer. Incidence rate ratios (IRR) were estimated by Poisson regression analysis of person-years at risk. The risk of epithelial ovarian cancer decreased with an increasing number of full-term pregnancies (IRR = 0.56, 95 percent confidence interval = 0.48-0.67 for three pregnancies cf one). However, no further reduction in risk was seen after the third pregnancy. The association with parity became weaker with increasing age at last birth. Further, the reduction in risk among parous women compared with nulliparous women was more pronounced shortly after birth. Both higher age at last birth and shorter time since last birth were associated with a reduction in risk, although these relations were seen mainly for the first and second births. Increasing age at first birth was associated with a decrease in risk among uniparous women but not among multiparous women. Our results indicate that the relations between the incidence of epithelial ovarian cancer and reproductive factors are more complex than previously believed.

Adult↗
PubMed1996

Birth characteristics and risk of Wilms' tumour: a nationwide prospective study in Norway.

Relationships between incidence of Wilms' tumour and information recorded at birth were investigated in a prospective study of the 1,489,297 children born in Norway between 1967 and 1992. A total of 119 individuals were diagnosed with Wilms' tumour in the age interval 0-14 years. A high length at birth was significantly associated with a high risk (incidence rate ratio 1.8 for length > or = 53 cm vs < or = 49 cm, 95% CI 1.0-3.2). A low Apgar score at 1 min was also associated with an increased risk (incidence rate ratio 2.2 for Apgar score < or = 8 vs a score > or = 9, 95% CI 1.2-3.9). For all variables for which an association was indicated, the association seemed to be restricted mainly to children aged less than 2 years. This suggests that Wilms' tumour diagnosed early in life may differ aetiologically from that of cases diagnosed later.

Adolescent↗
PubMed1995

Is the risk of cancer of the corpus uteri reduced by a recent pregnancy? A prospective study of 765,756 Norwegian women.

We have examined the relations between the incidence of cancer of the corpus uteri and pregnancies in a cohort of 765,756 Norwegian women, contributing a total of 9,307,118 person-years in the age interval 30-56 years. Incidence rate ratios (IRR) were calculated by Poisson regression analyses of person-years at risk. Separate analyses were carried out for the 2 main histological subtypes, endometrial carcinomas (554 cases) and sarcomas (112 cases). We observed a decrease in risk of endometrial carcinoma with an increasing number of full-term pregnancies (p < 0.001). The reduction in risk associated with the first pregnancy was more pronounced than that observed for any subsequent pregnancy. The risk of endometrial carcinoma increased with increasing time since last birth (IRR = 1.20, 95% CI = 1.08-1.34 per 5-year time interval). The reduction in risk among parous women compared to nulliparous women diminished with increasing time since last birth. For endometrial carcinoma, the decrease in risk with increasing age at first and last birth disappeared after adjustment for time since last birth. For sarcomas, however, the relation with age at births remained in analyses adjusted for time since birth, and time since birth seemed to be of minor importance as an independent risk factor. Our results support the hypothesis that the reduction in risk of endometrial carcinoma associated with a pregnancy is related to a mechanical shed of malignant or pre-malignant cells at each delivery.

Adult↗
PubMed1995

Multiple births, sex of children and subsequent breast-cancer risk for the mothers: a prospective study in Norway.

Endocrinological changes occurring during pregnancy may influence the subsequent cancer risk of the mother. Further, the endocrinological milieu may differ according to different birth characteristics. In the present study possible relations between multiple births, sex of children and breast-cancer risk were examined in a population-based, prospective study of 802,269 parous Norwegian women aged 20-56 years. A total of 4,782 women were diagnosed with breast cancer during follow-up. Of these, 97 had ever experienced a multiple birth. We found a slightly lower risk of breast cancer among women ever having had a multiple birth than among women with singletons only (IRR = 0.89, 95% CI = 0.73-1.09). The reduction in risk was mainly observed among women with a multiple last birth. Further, the reduction in risk seemed to diminish with increasing parity, and among women with 4 or more full-term pregnancies, ever having had a multiple birth was associated with an elevated risk (IRR = 1.48, 95% CI = 0.97-2.25). The sex of the first or last child did not affect the subsequent breast-cancer risk. Further, we found no associations with the sex distribution among all children or in multiple births, despite a tendency toward a reduced risk among women with several daughters only.

Adult↗