Johanna E. Torfadottir

Milk Intake in Early Life and Risk of Advanced Prostate Cancer

The authors investigated whether early-life residency in certain areas of Iceland marked by distinct differences in milk intake was associated with risk of prostate cancer in a population-based cohort of 8,894 men born between 1907 and 1935. Through linkage to cancer and mortality registers, the men were followed for prostate cancer diagnosis and mortality from study entry (in waves from 1967 to 1987) through 2009. In 2002-2006, a subgroup of 2,268 participants reported their milk intake in early, mid-, and current life. During a mean follow-up period of 24.3 years, 1,123 men were diagnosed with prostate cancer, including 371 with advanced disease (stage 3 or higher or prostate cancer death). Compared with early-life residency in the capital area, rural residency in the first 20 years of life was marginally associated with increased risk of advanced prostate cancer (hazard ratio = 1.29, 95% confidence interval (CI): 0.97, 1.73), particularly among men born before 1920 (hazard ratio = 1.64, 95% CI: 1.06, 2.56). Daily milk consumption in adolescence (vs. less than daily), but not in midlife or currently, was associated with a 3.2-fold risk of advanced prostate cancer (95% CI: 1.25, 8.28). These data suggest that frequent milk intake in adolescence increases risk of advanced prostate cancer.

Consumption of Fish Products across the Lifespan and Prostate Cancer Risk

Objective To examine whether fish and fish oil consumption across the lifespan is associated with a lower risk of prostate cancer. Design The study was nested among 2268 men aged 67–96 years in the AGES-Reykjavik cohort study. In 2002 to 2006, dietary habits were assessed, for early life, midlife and later life using a validated food frequency questionnaire. Participants were followed for prostate cancer diagnosis and mortality through 2009 via linkage to nationwide cancer- and mortality registers. Adjusting for potential confounders, we used regression models to estimate odds ratios (ORs) and hazard ratios (HRs) for prostate cancer according to fish and fish oil consumption. Results Among the 2268 men, we ascertained 214 prevalent and 133 incident prostate cancer cases, of which 63 had advanced disease. High fish consumption in early- and midlife was not associated with overall or advanced prostate cancer. High intake of salted or smoked fish was associated with a 2-fold increased risk of advanced prostate cancer both in early life (95% CI: 1.08, 3.62) and in later life (95% CI: 1.04, 5.00). Men consuming fish oil in later life had a lower risk of advanced prostate cancer [HR (95%CI): 0.43 (0.19, 0.95)], no association was found for early life or midlife consumption. Conclusions Salted or smoked fish may increase risk of advanced prostate cancer, whereas fish oil consumption may be protective against progression of prostate cancer in elderly men. In a setting with very high fish consumption, no association was found between overall fish consumption in early or midlife and prostate cancer risk.

Physical Activity from Early Adulthood and Risk of Prostate Cancer: A 24-Year Follow-Up Study among Icelandic Men.

Physical activity in adult life may reduce prostate cancer risk. Data are scarce on the role of activity during early adulthood, as well as combined recreational and occupational physical activity on prostate cancer risk and mortality. We undertook a prospective study of 8,221 Icelandic men (born 1907 to 1935) in the population-based Reykjavik Study. At enrollment, between 1967 and 1987, the men provided information on regular recreational physical activity since the age of 20 years as well as current occupational activity. Through linkage to nationwide cancer and mortality registers, the men were followed for prostate cancer diagnosis and mortality through 2009. We used Cox models to calculate the relative risk of prostate cancer by level of physical activity. During a mean follow-up of 24.8 years, 1,052 men were diagnosed with prostate cancer, of whom 349 had advanced disease (stage 3+ or prostate cancer death). Neither recreational nor occupational physical activity was, independently or combined, associated with overall or localized prostate cancer. Compared with physically inactive men, we observed a nonsignificant lower risk of advanced prostate cancer [HR, 0.67; 95% confidence interval (CI), 0.42–1.07] among men reporting both recreational and occupational physical activities (P value for interaction = 0.03). Awaiting confirmation in larger studies with detailed assessment of physical activity, our data suggest that extensive physical activity beginning in early adulthood may reduce the risk of advanced prostate cancer. Cancer Prev Res; 8(10); 905–11. ©2015 AACR.

Early life residence, fish consumption and risk of breast cancer.

Background: Little is known about fish intake throughout the life course and the risk of breast cancer. Methods: We used data on the first residence of 9,340 women born 1908 to 1935 in the Reykjavik Study as well as food frequency data for different periods of life from a subgroup of the cohort entering the Age, Gene/Environment Susceptibility (AGES)-Reykjavik Study (n = 2,882). Results: During a mean follow-up of 27.3 years, 744 women were diagnosed with breast cancer in the Reykjavik Study. An inverse association of breast cancer was observed among women who lived through the puberty period in coastal villages, compared with women residing in the capital area [HR, 0.78; 95% confidence interval (CI), 0.61–0.99]. In the subgroup analysis of this Icelandic population, generally characterized by high fish intake, we found an indication of lower risk of breast cancer among women with high fish consumption (more than 4 portions per week) in adolescence (HR, 0.71; 95% CI, 0.44–1.13) and midlife (HR, 0.46; 95% CI, 0.22–0.97), compared with low consumers (2 portions per week or less). No association was found for fish liver oil consumption in any time period, which could be due to lack of a reference group with low omega-3 fatty acids intake in the study group. Conclusions: Our findings suggest that very high fish consumption in early to midlife may be associated with a reduced risk of breast cancer. Impact: Very high fish consumption in early adulthood to midlife may be associated with decreased risk of breast cancer. Cancer Epidemiol Biomarkers Prev; 26(3); 346–54. ©2016 AACR.

Midlife metabolic factors and prostate cancer risk in later life

Metabolic syndrome is associated with several cancers, but evidence for aggressive prostate cancer is sparse. We prospectively investigated the influence of metabolic syndrome and its components on risk of total prostate cancer and measures of aggressive disease in a cohort of Icelandic men. Men in the Reykjavik Study (n = 9,097, enrolled 1967–1987) were followed for incident (n = 1,084 total; n = 378 advanced; n = 148 high‐grade) and fatal (n = 340) prostate cancer until 2014. Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for (1) measured metabolic factors at cohort entry (body mass index (BMI), blood pressure, triglycerides, fasting blood glucose) and (2) a metabolic syndrome score (range 0–4) combining the risk factors: BMI ≥30 kg/m2; systolic blood pressure (SBP) ≥130 or diastolic blood pressure (DBP) ≥85 mm Hg or taking antihypertensives; triglycerides ≥150 mg/dl; fasting blood glucose ≥100 mg/dl or self‐reported type 2 diabetes. Hypertension and type 2 diabetes were associated with a higher risk of total, advanced, high‐grade, and fatal prostate cancer, independent of BMI. Neither BMI nor triglycerides were associated with prostate cancer risk. Higher metabolic syndrome score (3–4 vs 0) was associated with a higher risk of fatal prostate cancer (HR 1.55; 95% CI: 0.89, 2.69; p trend = 0.08), although this finding was not statistically significant. Our findings suggest a positive association between midlife hypertension and diabetes and risk of total and aggressive prostate cancer. Further, metabolic syndrome as a combination of factors was associated with an increased risk of fatal prostate cancer.

Health Behavior and Metabolic Risk Factors Associated with Normal Weight Obesity in Adolescents.

Objective To explore health behaviors and metabolic risk factors in normal weight obese (NWO) adolescents compared with normal weight lean (NWL) peers. Design and Methods A cross-sectional study of 18-year-old students (n = 182, 47% female) in the capital area of Iceland, with body mass index within normal range (BMI, 18.5–24.9 kg/m2). Body composition was estimated via dual energy X-ray absorptiometry, fitness was assessed with maximal oxygen uptake (VO2max) during treadmill test, dietary intake through 24-hour recall, questionnaires explained health behavior and fasting blood samples were taken. NWO was defined as normal BMI and body fat >17.6% in males and >31.6% in females. Results Among normal weight adolescents, 42% (n = 76) were defined as NWO, thereof 61% (n = 46) male participants. Fewer participants with NWO were physically active, ate breakfast on a regular basis, and consumed vegetables frequently compared with NWL. No difference was detected between the two groups in energy- and nutrient intake. The mean difference in aerobic fitness was 5.1 ml/kg/min between the groups in favor of the NWL group (p<0.001). NWO was positively associated with having one or more risk factors for metabolic syndrome (Odds Ratio OR = 2.2; 95% confidence interval CI: 1.2, 3.9) when adjusted for sex. High waist circumference was more prevalent among NWO than NWL, but only among girls (13% vs 4%, p = 0.019). Conclusions High prevalence of NWO was observed in the study group. Promoting healthy lifestyle with regard to nutrition and physical activity in early life should be emphasized regardless of BMI.

Dietary habits in adolescence and midlife and risk of breast cancer in older women

Recent studies indicate that lifestyle factors in early life affect breast cancer risk. We therefore explored the association of high consumption of meat, milk, and whole grain products in adolescence and midlife, on breast cancer risk. We used data from the population based AGES-Reykjavik cohort (2002–2006), where 3,326 women with a mean age of 77 years (SD 6.0) participated. For food items and principal component derived dietary patterns we used Cox proportional models to calculate multivariate hazard ratios (HR) with 95% confidence intervals (95% CI). During a mean follow-up of 8.8 years, 97 women were diagnosed with breast cancer. For both adolescence and midlife, daily consumption of rye bread was positively associated with breast cancer (HR 1.7, 95% CI 1.1–2.6 and HR 1.8, 95% CI 1.1–2.9, respectively). In contrast, persistent high consumption of oatmeal was negatively associated with breast cancer (0.4, 95% CI 0.2–0.9). No association was found for other food items or dietary patterns that included rye bread. High rye bread consumption in adolescence and midlife may increase risk of late-life breast cancer whilst persistent consumption of oatmeal may reduce the risk.

The Relation of Type 2 Diabetes and Breast Cancer Incidence in Asian, Hispanic and African American Populations—A Review

In addition to rising type 2 diabetes and breast cancer incidence rates worldwide, diabetes may also increase breast cancer risk, and the association may vary by ethnicity. This review summarizes published data evaluating the association between diabetes and breast cancer in women of Asian, Hispanic and African American ancestry while considering a measure of obesity, body mass index (BMI). Published reports were identified through a search of PubMed and previous publications. Of 15 age-adjusted studies, 11 reported on Asian women from various countries, 3 on Hispanics and 1 on African Americans. The studies of Asian women described significant associations in 8 reports, with risk estimates of 1.5 to 8.4, but 3 were case-control studies and 6 did not adjust for BMI. The 3 case-control studies of Hispanic people included BMI, but only 1 detected a weak association between diabetes and breast cancer risk and was limited to postmenopausal women. The only study of African American women was a prospective cohort, and it showed no significant association between diabetes and breast cancer. In contrast to a 10% to 20% higher risk for breast cancer associated with diabetes reported for Caucasian women, there is little evidence for an association in Hispanics and African Americans. Although several studies of Asian women included in our review reported a higher risk for breast cancer with diabetes, methodologic shortcomings, such as lack of adjustment for obesity, use of a general population as controls, case-control design and small sample sizes, raise questions about the validity of the findings.

Fish and fish-liver oil consumption in adolescence and midlife and risk of CHD in older women.

OBJECTIVE To study the association of fish and fish-liver oil consumption across the lifespan with CHD later in life among Icelandic women, with special emphasis on the effects of consumption in adolescence. DESIGN Prevalence association study. Logistic regression was used to estimate odds ratios and 95 % confidence intervals of CHD according to fish or fish-liver oil exposure. Models were adjusted for age, education, concurrent diet and other known risk factors. SETTING The study was nested within the AGES-Reykjavik Study, conducted in Reykjavik, Iceland. SUBJECTS Participants were 3326 women aged 66-96 years, with available information on CHD status at entry to the study and information on fish and fish-liver oil consumption during midlife and adolescence. Dietary habits were assessed retrospectively using a validated FFQ. RESULTS CHD was identified in 234 (7·9 %) women. Compared with women with no intake of fish-liver oil in adolescence or midlife, women who consumed fish-liver oil at least three times weekly in adolescence or in midlife had a decreased risk of CHD (OR=0·62; 95 % CI 0·45, 0·85 and OR=0·68; 95 % CI 0·50, 0·94, respectively). No associations were observed between fish intake (>2 portions/week v. ≤2 portions/week) in adolescence or midlife and CHD in this population with high fish intake. CONCLUSIONS Fish-liver oil consumption, from early life, may reduce the risk of CHD in older women. Lifelong nutrition may be of importance in the prevention of CHD in older women.

Correction: Dietary habits in adolescence and midlife and risk of breast cancer in older women

[This corrects the article DOI: 10.1371/journal.pone.0198017.].