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Karin B Michels

Publications and source records attributed to Karin B Michels.

At least 19 recordsLinked to original sources
PubMed2006

Longitudinal study on the role of body size in premenopausal breast cancer.

BACKGROUND: A high body mass index (BMI) has been related to a reduced risk of breast cancer in premenopausal women. The mechanisms underlying this association have not been elucidated. METHODS: We explored whether factors affecting ovulation may explain the inverse association between BMI (calculated as weight in kilograms divided by the square of height in meters) and breast cancer in 113,130 premenopausal participants in the Nurses' Health Study II. During 1,225,520 person-years of prospective follow-up between 1989 and 2003, 1398 incident cases of invasive breast cancer were diagnosed. Weight, height, ovulatory infertility, menstrual cycle patterns, and a multitude of covariates were assessed throughout follow-up. Cox proportional hazards regression was used to compute hazard ratios and 95% confidence intervals (CIs). RESULTS: We observed a significant linear inverse trend between current BMI and breast cancer incidence (P<.001) that was not explained by menstrual cycle characteristics or infertility due to an ovulatory disorder (covariate-adjusted hazard ratio for breast cancer in women with a BMI > or =30 vs 20.0-22.4, 0.81; 95% CI, 0.68-0.96). We found BMI at age 18 years to be the strongest predictor of breast cancer incidence (covariate-adjusted hazard ratio for breast cancer in women with a BMI at age 18 years > or =27.5 vs 20.0-22.4, 0.57; 95% CI, 0.41-0.81). CONCLUSIONS: Body size during the early phases of adult life seems to be particularly important in the development of premenopausal breast cancer. Factors other than anovulation are likely to mediate the protection conferred by a high BMI.

Adult↗
PubMed2006

Parental age at delivery and incidence of breast cancer: a prospective cohort study.

BACKGROUND: Studies on parental age at delivery in relation to breast cancer risk have had mixed results, but prospective data are limited. No study has explored the associations with subtypes of breast cancer defined by hormonal receptor status. METHODS: 109,773 women in the Nurses' Health Study were followed from 1976 to 2002. We used Cox proportional hazards model to examine the association between parental age at delivery and daughters' risk of breast cancer. RESULTS: 6,827 incident cases of invasive breast cancer occurred in this cohort during 2,581,098 person-years. Adjusting for other early life exposures and family history of breast cancer, the hazard ratio for breast cancer in women born to mothers aged 21-25, 26-30, 31-35, and > or =36 years was, respectively, 1.08 (95% CI: 0.99-1.18), 1.12 (95% CI: 1.03-1.23), 1.17 (95% CI: 1.06-1.29), and 1.12 (95% CI: 1.01-1.25), compared to women born to mothers aged < or =20 years (P for trend = 0.008). Similarly, advanced paternal age was associated with increased incidence of breast cancer (P for trend = 0.03), but the association disappeared when conditioning on maternal age. The positive association between maternal age and incidence of breast cancer was stronger for estrogen receptor-positive and progesterone receptor-positive tumors (P for trend = 0.003) than for tumors with both receptors negative (P for trend = 0.78), and was more consistent among postmenopausal women, women without a family history and women who were first born. CONCLUSION: Our findings support a modest positive association between maternal age and daughter's risk of breast cancer, possibly mediated by hormonal factors.

Adult↗
PubMed2006

Role of birthweight in the etiology of breast cancer.

Breast cancer may originate in utero. We reviewed the available evidence on the association between birthweight and the risk of breast cancer. To date, 26 research papers addressing this issue have been published. The majority of studies identified a positive link between birthweight and premenopausal, but not postmenopausal, breast cancer. The relative risk estimate for breast cancer comparing women with high birthweight to women with low birthweight combining all studies including both pre- and postmenopausal breast cancer was 1.23 (95% confidence interval 1.13-1.34). The mechanisms underlying this association likely include elevated levels of growth factors that may increase the number of susceptible stem cells in the mammary gland or initiate tumors through DNA mutations. Loss of imprinting (LOI) of growth hormone genes relevant for intrauterine growth, such as insulin-like growth factor 2 (IGF2), leads to abnormally high levels of these hormones evidenced by high birthweight. LOI of IGF2 has also been found in mammary tumor tissue. The role of environmental factors that stimulate such epigenetic regulation of gene expression remains to be elucidated.

Birth Weight↗
PubMed2006

Adult height, age at attained height, and incidence of breast cancer in premenopausal women.

Adult height has been positively associated with breast cancer risk in epidemiologic studies, and recent evidence suggests that the timing and rate of growth may also influence risk. We examined both adult height and age at attained height, an indicator of the timing of the pubertal growth spurt, in relation to incidence of premenopausal breast cancer in the Nurses' Health Study II. Participants were 108,829 premenopausal women who reported their height in 1989; of these, 37,572 provided information on their age at attained height on a later supplementary questionnaire. During 12 years of follow-up, 1,041 cases of invasive breast cancer were identified (402 with age at attained height). Cox proportional hazards models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs). Adult height was positively associated with breast cancer incidence; the multivariate RR for participants 1.75 m or taller compared to those shorter than 1.60 m was 1.57 (95% CI: 1.23-2.01, p trend < 0.0001), and each 5-cm increment corresponded to an 11% increase in risk (95% CI: 6-17%). There was no overall association for age at attained height, however, with a multivariate RR of 0.96 (95% CI: 0.66-1.39) for women who attained their maximum height at age 18 or older compared to those who reached it before age 14 (p trend = 0.65). These results confirm previous findings that taller adult height is associated with increased risk of premenopausal breast cancer but do not provide evidence that age at attained height is related to risk.

Adolescent↗
PubMed2006

Longitudinal study of birthweight and the incidence of breast cancer in adulthood.

A high birthweight has been associated with an increased risk of breast cancer later in life. The role of adult variables, possible effect modifiers and cancer characteristics has been little studied. We explored these in two large prospective cohort studies of women, the Nurses' Health Study (NHS) and the Nurses' Health Study II (NHS II). We collected information on birthweight from 152,608 female nurses participating in NHS and NHS II. During 10 years and 1.3 million person-years of follow-up, invasive breast cancer was newly diagnosed among 828 premenopausal and 2312 postmenopausal women. Data were analyzed using a Cox proportional hazards model. Premenopausal women with a birthweight of <5.5 lbs had a covariate-adjusted hazard ratio (HR) for breast cancer of 0.66 [95% confidence interval (CI) 0.47-0.93] compared with women born at 8.5 lbs or above. Adult height was the only factor explaining some of the association between birthweight and breast cancer incidence; after adjustment for height the HR was 0.73 (95% CI 0.51-1.03). The association between birthweight and the incidence of breast cancer was stronger among women with estrogen-receptor positive and progesterone-receptor positive breast cancer. Among postmenopausal women, no important association between the birthweight and the incidence of breast cancer was detected (HR comparing women with a birthweight of 5.5 lbs or less with women with a birthweight>8.5 lbs: 0.97; 95% CI 0.80-1.16). In these two large prospective cohorts, a low birthweight was associated with a decreased incidence of breast cancer among premenopausal women. This association was independent of other factors operating later in life, except for adult height.

Adult↗
PubMed2006

A prospective study on habitual duration of sleep and incidence of breast cancer in a large cohort of women.

Mounting evidence suggests habitual sleep duration is associated with various health outcomes; both short and long sleep duration have been implicated in increased risk of cardiovascular disease, diabetes, and all-cause mortality. However, data on the relation between sleep duration and cancer risk are sparse and inconclusive. A link between low levels of melatonin, a hormone closely related to sleep, and increased risk of breast cancer has recently been suggested but it is unclear whether duration of sleep may affect breast cancer risk. We explored the association between habitual sleep duration reported in 1986 and subsequent risk of breast cancer in the Nurses' Health Study using Cox proportional hazards models. During 16 years of follow-up, 4,223 incident cases of breast cancer occurred among 77,418 women in this cohort. Compared with women sleeping 7 hours, covariate-adjusted hazard ratios and 95% confidence intervals for those sleeping < or =5, 6, 8, and > or =9 hours were 0.93 (0.79-1.09), 0.98 (0.91-1.06), 1.05 (0.97-1.13), and 0.95 (0.82-1.11), respectively. A moderate trend in risk increase towards longer sleep duration was observed when analyses were restricted to participants who reported same sleep duration in 1986 and 2000 (P(trend) = 0.05). In this prospective study, we found no convincing evidence for an association between sleep duration and the incidence of breast cancer.

Adult↗
PubMed2006

A prospective study of breast size and premenopausal breast cancer incidence.

Studies of the association between breast size, as a proxy for mammary gland mass, and breast cancer risk have given equivocal results. Most have been case-control studies with limited statistical power. We conducted a prospective analysis of the relation between breast size as measured by self-reported bra cup size and breast cancer risk among premenopausal women enrolled in the Nurses' Health Study II. Bra cup size at age 20 was assessed among 89,268 premenopausal women aged 29-47 in 1993. Subsequent incident cases of invasive breast cancer were assessed until 2001. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated with a Cox proportional hazards model adjusting for potential confounders and risk factors for breast cancer. During 622,732 person-years of follow-up, 803 premenopausal women were newly diagnosed with invasive breast cancer. For women with a BMI below 25 kg/m2, those with a bra cup size of "D or larger" had a significantly higher incidence of breast cancer than women who reported "A or smaller" (covariate adjusted HR=1.80; 95% CI 1.13-2.88; ptrend=0.01). There was no significant association among women with a BMI of 25 kg/m2 or higher. Stratifying by BMI at age 18 at a cutoff point of 21 kg/m2 gave similar results. Larger bra cup size at a young age is associated with a higher incidence of premenopausal breast cancer, though this association is limited to leaner women.

Adult↗
PubMed2006

Fruit and vegetable consumption and colorectal adenomas in the Nurses' Health Study.

Consumption of fruits and vegetables may confer protection from colorectal adenomas, but the limited observational and interventional evidence is inconclusive. We examined the association between fruit and vegetable consumption and the prevalence and incidence of adenomas of the distal colon and rectum in the Nurses' Health Study (NHS). We used data from 34,467 women in the NHS who had undergone colonoscopy or sigmoidoscopy during follow-up between 1980 and 1998. Consumption of fruits and vegetables was assessed in 1980, 1984, 1986, 1990, and 1994 using a semiquantitative food frequency questionnaire; 1,720 prevalent cases of adenoma of the distal colon and rectum were diagnosed between 1980 and 1998. Frequent consumption of fruit was inversely related to the risk of being diagnosed with polyps, whereas little association was found for vegetable consumption. Women who reported consuming five or more servings of fruit a day had an odds ratio (OR) of 0.60 [95% confidence interval (95% CI), 0.44-0.81] for developing colorectal adenomas compared with women who consumed only one or fewer servings of fruit per day, after adjustment for relevant covariates (P(trend) = 0.001). The respective OR for vegetable consumption was 0.82 (95% CI, 0.65-1.05; P(trend) = 0.1). Women who consumed four or more servings of legumes per week had a lower incidence of colorectal adenomas than women who reported consuming one serving per week or less (OR, 0.67; 95% CI, 0.51-0.90; P(trend) = 0.005). Frequent consumption of fruit may reduce the risk of colorectal adenomas.

Adenoma↗
PubMed2006

Preschool diet and adult risk of breast cancer.

Events before puberty may affect adult risk of breast cancer. We examined whether diet during preschool age may affect a woman's risk of breast cancer later in life. We conducted a case-control study including 582 women with breast cancer and 1,569 controls free of breast cancer selected from participants in the Nurses' Health Study and the Nurses' Health Study II. Information concerning childhood diet of the nurses at ages 3-5 years was obtained from the mothers of the participants with a 30-item food-frequency questionnaire. An increased risk of breast cancer was observed among woman who had frequently consumed French fries at preschool age. For one additional serving of French fries per week, the odds ratio (OR) for breast cancer adjusted for adult life breast cancer risk factors was 1.27 (95% confidence interval [CI] = 1.12-1.44). Consumption of whole milk was associated with a slightly decreased risk of breast cancer (covariate-adjusted OR for every additional glass of milk per day = 0.90; 95% CI = 0.82-0.99). Intake of none of the nutrients calculated was related to the risk of breast cancer risk in this study. These data suggest a possible association between diet before puberty and the subsequent risk of breast cancer. Differential recall of preschool diet by the mothers of cases and controls has to be considered as a possible explanation for the observed associations. Further studies are needed to evaluate whether the association between preschool diet and breast cancer is reproducible in prospective data not subject to recall bias.

Adolescent↗
PubMed2006

Defibulation to treat female genital cutting: effect on symptoms and sexual function.

OBJECTIVE: Women who have undergone type III female genital cutting may suffer long-term complications. Defibulation (reconstructive surgery of the infibulated scar) can alleviate some of these complications. We studied the physical and sexual outcomes after defibulation and evaluated both patient and husband satisfaction. METHODS: The medical records of 40 consecutive women with a history of type III female genital cutting who underwent defibulation between 1995 and 2003 were reviewed. Data collected included demographics, indications for the procedure, closure type, intraoperative and postoperative complications. Telephone surveys were conducted between 6 months and 2 years postprocedure to evaluate the long-term health and sexual satisfaction outcomes. RESULTS: Of 40 women identified as having undergone defibulation, 95% were Somali, 65% were married, and 73% were between the ages of 19 and 30. Primary indications for defibulation were being pregnant (30%), dysmenorrhea (30%), apareunia (20%), and dyspareunia (15%). Secondary indications were apareunia (20%), difficulty urinating (12.5%), and dyspareunia (10%). Sixty-five percent had a subcuticular repair. Forty-eight percent had an intact clitoris buried beneath the scar. None had intraoperative or postoperative complications. Of the 32 patients reached by telephone, 94% stated they would highly recommend it to others. One hundred percent of patients and their husbands were satisfied with the results, felt their appearance had improved, and were sexually satisfied. CONCLUSION: Defibulation is recommended for all infibulated women who suffer long-term complications. The complication rates are minimal, with high satisfaction rates among patients and their husbands. LEVEL OF EVIDENCE: II-3.

Adult↗
PubMed2006

Birthweight and body size throughout life in relation to sex hormones and prolactin concentrations in premenopausal women.

The association of birthweight and body size throughout life with premenopausal breast cancer risk may be due, in part, to relationships with sex hormones. Therefore, we assessed whether birthweight, body shape at ages 5 and 10, body mass index (BMI) at age 18 and adulthood, adult waist circumference and waist-to-hip ratio (WHR), and attained height were associated with the plasma concentrations of estrogens, androgens, progesterone, prolactin, and sex hormone-binding globulin (SHBG) in 592 premenopausal women, ages 33 to 52 years old, from the Nurses' Health Study II. About 85% of women provided blood samples during follicular and luteal menstrual phases; other women had a single untimed sample. We observed few associations between sex hormone levels and birthweight or body shape in childhood. However, adult BMI was inversely associated with SHBG (P trend < 0.001) and positively associated with free testosterone (P trend < 0.001) concentrations. Adult BMI was not associated with follicular or luteal free estradiol levels (P trend >or= 0.15) because it was inversely associated with total estradiol levels (P trend < 0.001 for follicular and luteal estradiol levels). Testosterone, androstenedione, and progesterone were inversely associated with BMI. Comparing women with a BMI of >or=30 versus <20 kg/m2, levels were higher by 53% for free testosterone and lower by 51% for SHBG, 39% for follicular estradiol, 20% for luteal estradiol, 14% for androstenedione, 13% for testosterone, and 20% for progesterone. We observed no clear associations between BMI at age 18, waist circumference, WHR, or height, and sex hormone concentrations. Our results suggest that effects on premenopausal sex hormone levels may be one mechanism through which adult adiposity, but not birthweight or childhood body size, affects premenopausal breast cancer risk.

Adult↗
PubMed2005

Duration of lactation and incidence of type 2 diabetes.

CONTEXT: Lactation is associated with improved glucose and insulin homeostasis, independent of weight change. OBJECTIVE: To evaluate the association between lactation history and incidence of type 2 diabetes. DESIGN, SETTING, AND PARTICIPANTS: Prospective observational cohort study of 83,585 parous women in the Nurses' Health Study (NHS) and retrospective observational cohort study of 73,418 parous women in the Nurses' Health Study II (NHS II). MAIN OUTCOME MEASURE: Incident cases of type 2 diabetes mellitus. RESULTS: In the NHS, 5145 cases of type 2 diabetes were diagnosed during 1,239,709 person-years of follow-up between 1986 and 2002, and in the NHS II, 1132 cases were diagnosed during 778,876 person-years of follow-up between 1989 and 2001. Among parous women, increasing duration of lactation was associated with a reduced risk of type 2 diabetes. For each additional year of lactation, women with a birth in the prior 15 years had a decrease in the risk of diabetes of 15% (95% confidence interval, 1%-27%) among NHS participants and of 14% (95% confidence interval, 7%-21%) among NHS II participants, controlling for current body mass index and other relevant risk factors for type 2 diabetes. CONCLUSIONS: Longer duration of breastfeeding was associated with reduced incidence of type 2 diabetes in 2 large US cohorts of women. Lactation may reduce risk of type 2 diabetes in young and middle-aged women by improving glucose homeostasis.

Adult↗
PubMed2005

Smoking and other lifestyle factors and the risk of Graves' hyperthyroidism.

BACKGROUND: Hyperthyroidism caused by Graves' disease is common in women, yet little is known about risk factors for the disease. We sought to determine whether lifestyle factors, including smoking, alcohol consumption, physical activity level, and body mass index, are risk factors for Graves' hyperthyroidism. METHODS: This analysis was conducted using data from the Nurses' Health Study II, among 115109 women aged 25 to 42 at entry. Incident reports of women with Graves' hyperthyroidism, confirmed to have the disorder, were included. RESULTS: During 1 328 270 person-years of follow-up, incident diagnoses of Graves' hyperthyroidism were confirmed in 543 women; the 12-year incidence was 4.6 per 1000 women. Cigarette smoking was a predictor of Graves' hyperthyroidism. The hazard ratio among current smokers was 1.93 (95% confidence interval [CI], 1.54-2.43), and among past smokers it was 1.27 (95% CI, 1.03-1.56), after adjusting for recent pregnancy, parity, and other variables. Among current smokers, the hazard ratio increased with the intensity of smoking and was 2.63 (95% CI, 1.71-4.04) among women who smoked 25 or more cigarettes daily. Obesity was associated with a decreased risk of Graves' hyperthyroidism. The hazard ratio for the disorder among women with a body mass index of 30 kg/m(2) or higher was 0.68 (95% CI, 0.49-0.92). Alcohol intake and physical activity level were not associated with risk of Graves' hyperthyroidism. CONCLUSIONS: Smoking is a risk factor for Graves' hyperthyroidism in women. Obesity may be associated with a reduced risk, although weight loss as the first manifestation of hyperthyroidism cannot be excluded.

Adult↗
PubMed2005

Measurement of fruit and vegetable consumption with diet questionnaires and implications for analyses and interpretation.

Measurement error can have an important impact on the estimation of the true relation between diet and disease. The authors examined the performance of models regressing plasma vitamin C level on fruit and vegetable consumption and the effect of categorization of fruit and vegetable consumption on the association with plasma vitamin C. They used diet information reported by 4,487 participants in the Norfolk, United Kingdom, portion of the European Prospective Investigation into Cancer and Nutrition by means of a 7-day diet diary and a food frequency questionnaire (FFQ) (1993-1998). The authors found substantial differences in mean fruit and vegetable consumption assessed by the two diet instruments. Consumption estimated with the FFQ was about twice as high as that obtained with the 7-day diary, and the ranking of individuals according to estimates of fruit and vegetable consumption from the 7-day diary and the FFQ differed substantially. When fruit and vegetable consumption were categorized into quintiles, the two questionnaires produced similar associations of relative intake with plasma vitamin C, but estimation of the association of absolute intake with plasma vitamin C differed.

Aged↗
PubMed2005

Longitudinal study of birth weight and adult body mass index in predicting risk of coronary heart disease and stroke in women.

OBJECTIVES: To determine whether birth weight and adult body size interact to predict coronary heart disease in women, as has been observed for men. To determine whether birth weight and adult body size interact to predict risk of stroke. DESIGN: Longitudinal cohort study. SETTING AND PARTICIPANTS: 66,111 female nurses followed since 1976 who were born of singleton, term pregnancies and reported their birth weight in 1992. MAIN OUTCOME MEASURES: 1504 events of coronary heart disease (myocardial infarction or sudden cardiac death) and 1164 strokes. RESULTS: For each kilogram of higher birth weight, age adjusted hazard ratios from prospective analysis were 0.77 (95% confidence interval 0.69 to 0.87) for coronary heart disease and 0.89 (0.78 to 1.01) for total stroke. In combined prospective and retrospective analysis, hazard ratios were 0.84 (0.76 to 0.93) for total stroke, 0.83 (0.71 to 0.96) for ischaemic stroke, and 0.86 (0.66 to 1.11) for haemorrhagic stroke. Exclusion of macrosomic infants (> 4536 g) yielded stronger estimates. Risk of coronary heart disease was especially high for women who crossed from a low centile of weight at birth to a high centile of body mass index in adulthood. The association of lower birth weight with increased risk of stroke was apparent across categories of body mass index in adults and was not especially strong among heavier women. CONCLUSIONS: Higher body mass index in adulthood is an especially strong risk factor for coronary heart disease among women who were small at birth. In this large cohort of women, size at birth and adiposity in adulthood interacted to predict events of coronary heart disease but not stroke events.

Adolescent↗
PubMed2005

The role of nutrition in cancer development and prevention.

Nutrition has long been suspected to play an important role in cancer etiology. The biologic properties of nutrients make them prime candidates to aid in cancer prevention. Indeed, early epidemiologic cancer studies seemed to confirm the relevance of diet. These studies, however, were plagued by recall bias and confounding and may have thus been misleading. The results from large, prospective cohorts do not support a strong relation between nutrition and cancer. Given the difficulties in precisely assessing habitual diet, modest associations may exist, which may be impossible to capture when relying on self-reported dietary information. Energy balance, reflected in a low body weight and high level of physical activity, has been more convincingly related to lower cancer rates. The potential importance of more extreme dietary regimens and of nutrition during earlier periods of life remains to be explored. Finally, epigenetic research is likely to contribute to the understanding of nutritional regulation of gene expression.

Diet↗