Handedness and mortality risk in older women

Does Laterality in Breast Cancer still have the Importance to be Studied? A Meta-analysis of Patients with Breast Cancer

BACKGROUND

Breast cancer (BC) is one of the most common cancers in the world. Studies show that left-sided BC in pre and post-menopausal women leads to double the risk of worse morbidity and mortality and the reasons are uncertain. Finding the relationship between BC laterality and other possible risk factors can be advantageous for the prognosis of BC.

OBJECTIVE

This present study aimed to analyze the relationship between BC laterality and possible risk factors.

METHODS

A total of 6089 studies were screened. 23 studies from 1971 to 2021 met the inclusion criteria and were included in the meta-analysis. A pooled relative risk was generated via meta-analysis with a 95% confidence interval.

RESULTS

Left-side BC laterality was significant (p < 0.00001) in the women populations compared to the right side based on the pooled size with possible high-risk factors, including handedness, older women, body mass index, people with black skin, invasive type carcinoma, and estrogen receptor-negative BC. These findings suggest that there may be a complex interplay of genetic, environmental, and lifestyle factors that contribute to left-side BC laterality.

CONCLUSION

Results suggest an increased rate of BC on the left side, with high-risk factors contributing to BC laterality, which may be useful in predicting prognosis. This study provides significant insights into the relationship between high-risk factors and BC laterality. By identifying potential risk factors associated with left-side BC, it may be possible to improve the ability to predict prognosis and develop more targeted treatment strategies. This information could be particularly useful for healthcare providers and patients, as it may guide decisions regarding screening, prevention, and treatment, ultimately improving patient outcomes and reducing the overall burden of BC.

A large-scale population study of early life factors influencing left-handedness

Hand preference is a conspicuous variation in human behaviour, with a worldwide proportion of around 90% of people preferring to use the right hand for many tasks, and 10% the left hand. We used the large cohort of the UK biobank (~500,000 participants) to study possible relations between early life factors and adult hand preference. The probability of being left-handed was affected by the year and location of birth, likely due to cultural effects. In addition, hand preference was affected by birthweight, being part of a multiple birth, season of birth, breastfeeding, and sex, with each effect remaining significant after accounting for all others. Analysis of genome-wide genotype data showed that left-handedness was very weakly heritable, but shared no genetic basis with birthweight. Although on average left-handers and right-handers differed for a number of early life factors, all together these factors had only a minimal predictive value for individual hand preference.

Prenatal and early life factors and risk of Parkinson's disease

Few studies have investigated the relation between early life factors and risk of Parkinson's disease (PD), although a potential role of exposures during pregnancy and childhood has been hypothesized. The study population comprised participants in two prospective cohorts: the Nurses' Health Study (121,701 female nurses followed up from 1976-2002) and the Health Professionals Follow-up Study (51,529 male health professionals followed up from 1986-2002). PD risk was examined in relation to season of birth, birthweight, parental age at birth, preterm birth, multiple birth, ever having been breast-fed, and handedness. We identified 659 incident PD cases. No significant relation with PD was observed for birthweight, paternal age, preterm birth, multiple birth, and having been breast-fed. A modest nonsignificant association was suggested for season of birth (30% higher risk of PD associated with spring versus winter birth) and for older maternal age at birth (75% increased risk among those with mothers aged 30 years and older versus younger than 20 years). Left-handedness was associated with a 62% increased risk of PD in women but not in men. Further investigation of the relation between prenatal, perinatal, or neonatal factors and PD in other study populations is suggested.

The relationship between handedness and risk of multiple sclerosis

BACKGROUND

Left-handedness has been studied as a marker for in-utero exposure to sex steroid hormones, and an increased risk of autoimmune and immune disorders among left-handed individuals has been suggested.

OBJECTIVE

This study examines the relationship between hand preference and risk of multiple sclerosis, a presumed autoimmune disorder of unknown etiology.

METHODS

The study population comprised participants in the Nurses' Health Study, an ongoing prospective cohort study of 121,701 female nurses in the United States with followup from 1976 to 2002. The nurses were asked to report their natural hand preference (right, left, ambidextrous, forced to change).

RESULTS

During followup 210 incident cases with multiple sclerosis were confirmed. A 62% increased risk of multiple sclerosis was observed among women who were naturally left handed as compared to those who were naturally right handed (95% CI: 1.04-2.53).

CONCLUSIONS

This study suggests a modest increase in risk of multiple sclerosis among left-handed women. Further investigation of this relationship is suggested in other populations including both males and females. While the current results suggest that prenatal exposure to sex hormones may play a role in multiple sclerosis risk, direct examination of the relationship between in-utero hormone exposure and hand preference is necessary before any conclusions can be drawn.

Handedness and cognitive function in older men and women: a comparison of methods

OBJECTIVE

Previous studies of handedness and cognitive function rely on self-classification and yield inconsistent results. This study examines the associations of self-reported versus grip-strength-based handedness with cognitive function in healthy older men and women.

DESIGN

Cross-sectional study.

SETTING

1988-91 follow-up clinic visit and 1991 mailed survey.

PARTICIPANTS

684 men and 985 women aged 55-95 who were community dwelling.

MEASUREMENTS

Cognitive function was assessed with 12 tests and grip strength was measured by hand-held dynamometer. Self-reported handedness was obtained with a mailed survey.

RESULTS

By self-report, 92.1% of men and women were right-handed; 2.0% were left handed. By grip strength, in men, 64.3% were right-handed, 22.5% left-handed, and 13.2% ambidextrous. In women, 61.3% were right-handed, 17.3% left-handed, and 21.4% ambidextrous. No cognitive function differences were found by self-reported handedness in either sex (p's>0.10). However, based on grip strength, left-handed women scored poorer than right-handed or ambidextrous women in immediate and delayed memory, attention, and verbal fluency (p's<0.05). Using categorical definitions, left-handed or ambidextrous individuals based on grip strength were more likely to show poor cognitive function on 4 of 5 tests.

CONCLUSION

Grip strength is a useful alternative to self-reports for classifying handedness. Left-handedness by grip-strength, may be related to poorer cognitive function; this association may vary by gender.

Innate handedness and disease-specific mortality in women

BACKGROUND

Left-handedness has been reported to be associated with reduced life expectancy, but the evidence is far from conclusive.

METHODS

We studied the association between innate handedness and total mortality, as well as cause-specific mortality, in a cohort of 12,178 middle-aged Dutch women who were followed for almost 13 years. The relation between handedness and mortality was analyzed using Cox regression in a case-cohort approach, in which a random sample of 1500 women was used to represent person-years under observation for the entire cohort.

RESULTS

During a median follow-up of 12.6 years, 252 women died. Hazard ratios comparing left-handed women with other women were 1.4 for all-cause mortality (95% confidence interval = 0.9-2.0), 1.7 for total cancer mortality (1.0-2.7), 2.0 for breast cancer mortality (0.8-4.6), 4.6 for colorectal cancer mortality (1.5-14.3), 1.3 mortality from diseases of the circulatory system (0.5-3.3), and 3.7 for cerebrovascular mortality (1.1-12.1), after adjusting for potential confounders (socioeconomic status, age, body mass index, and cigarette smoking status at study recruitment).

CONCLUSIONS

Left-handedness is associated with higher mortality in women.

An examination of the hypothesis that left-handers die earlier: the Canadian Study of Health and Aging

The present paper is a prospective examination, using data from the Canadian Study of Health and Aging (CSHA-1 and CSHA-2), of the hypothesis that self-reported left-handers die earlier than right-handers. Persons over age 65 receiving a clinical evaluation in 1991 (n = 2786) as part of CSHA-1 were recontacted in 19956. At baseline, the sample showed a trend for the expected cross-generational decline in nonright-handedness with increasing age (3.2% of those aged 6574 reported being left-handers while 2.1% were left-handers in the 85+ age group). At follow-up, there were no significant differences in mortality between self-reported right-handers (52.6% died), left-handers (56.8%), and ambidexters (46.6%). The Odds Ratio was 1.18 (95% confidence interval 0.721.93) for left- compared to right-handers. There was no evidence that being left-handed increased the risk of death in this sample of elderly Canadians.

The effects of hand preference side and hand preference switch history on measures of psychological and physical well-being and cognitive performance in a sample of older adult right-and left-handers

Claims have been made that left-handedness often arises from pathological causes, and that owing to this underlying pathology, the presence of sinistrality may entail disadvantages for both the length and quality of life. A prime implication of these claims is that left-handers, as a group, should display signs of poorer fitness than right-handers. This poorer fitness might take the form of an increased incidence of illnesses and/or accidents. In addition, it might also be predicted that left-handers would experience a psychological and, perhaps, cognitive quality of life that is inferior to that of right-handers. In the present study, we measured a large sample (N=1277) of older adults on four indexes of lateral preference (hand, foot, eye, and ear), on whether or not they experienced pressure to switch their preferred writing hand, and variables related to psychological well-being, physical health, and cognitive performance. The results revealed that the presence of left hand writing, in isolation, did not predict decreases in quality of life factors; however, in conjunction with left-handed writing, the presence of a hand preference switch report was shown to be important. In particular, one subset of left-handers-those who attempted to change their preferred writing hand but were unsuccessful-was found to have a lower quality of psychological and physical well-being on multiple measures.

Left-handedness in relation to breast cancer risk in postmenopausal women

Breast cancer risk may be influenced by intrauterine exposure to steroid hormones. We evaluated left-handedness, a marker of intrauterine hormone exposure, in relation to breast cancer risk in our population-based, case-control study. Case women 50-79 years of age with a first diagnosis of invasive breast cancer were ascertained through statewide cancer registries in Wisconsin, Massachusetts, and New Hampshire. Control women were identified in each state through lists of licensed drivers (for ages 50-64) and Medicare beneficiaries (for ages 65-79), and selected at random to correspond with the age distribution of case women. Exposure information, including handedness, was obtained through a telephone interview. Our results indicated a modest association between left-handedness and breast cancer risk (OR = 1.42; 95% CI = 1.10-1.83). The effect of left-handedness was modified by age; we observed the greatest risk ratio in the oldest age group. Left-handedness was not associated with breast tumor laterality. Our results are consistent with the hypothesis that intrauterine hormone exposures play a role in the development of breast cancer.

The association between switching hand preference and the declining prevalence of left-handedness with age

OBJECTIVES

This study determined the prevalence of left-handedness and of switching hand preference among innately left-handed subjects.

METHODS

Subjects of Swiss nationality (n = 1692), participating in a population-based survey in Geneva, Switzerland, completed a questionnaire on innate hand preference and current hand preference for writing.

RESULTS

From 35 to 44 years of age to 65 to 74 years of age, the prevalence of innate left-handedness declined from 11.9% to 6.2% (trend P = .007). In these same age groups, the proportion of innately left-handed subjects who switched to the right hand for writing increased from 26.6% to 88.9% (trend P = .0001).

CONCLUSIONS

Across generations, we found an increase in the prevalence of switching hand preference among innately left-handed subjects. This phenomenon could be explained by social and parental pressure to use the right hand.

The epidemiology of left-handedness in a hospital population

PURPOSE

We evaluated the association between left-handedness (LH) and age, education, cigarette smoking, alcohol consumption, and disease status in a case-control study of 8801 hospitalized patients with cancer and those with other conditions.

METHODS

Subjects were interviewed in person using a structured questionnaire that contained detailed sections of lifestyle behaviors.

RESULTS

The overall prevalences of LH were 7.6% among men and 6.5% among women. Among both sexes LH declined with increasing age (P < 0.05). After adjustment for age, the following associations were observed. Men had a higher risk of LH than women. The prevalence of LH was lower in ever-married subjects compared with never-married subjects (odds ratio [OR] for men, 0.7; 95% confidence intervals [CI], 0.5-0.9; for women, OR, 0.5; 95% CI, 0.3-0.9). Among men, the prevalence of LH was not associated with race, years of education, smoking status, or levels of alcohol consumption. The risk of LH was elevated in men diagnosed with fractures as compared with all other male patients (OR, 2.4; 95% CI, 1.3-6.7). Among women, LH was not associated with race, smoking, or hormonal and reproductive factors, but LH was more common among female high-school and college graduates and among self-reported alcoholics. The odds ratio of LH was significantly lower in women with breast cancer (OR, 0.3; 95% CI, 0.1-0.7).

CONCLUSIONS

The increased risk of serious injuries in LH is not a result of higher alcohol use. Handedness might be an important factor in the safe use of industrial equipment.