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Breastfeeding has long been believed to protect against infection in infants, but protection against respiratory illnesses has not been consistently demonstrated in studies in developed countries. Between 1988 and 1992, the authors assessed the effect of breastfeeding on incidence and duration of respiratory illnesses during the first 6 months of life in a prospective study that actively tracked breastfeeding and respiratory illnesses. A cohort of 1,202 healthy infants, born in Albuquerque, New Mexico, between January 1, 1988 and June 30, 1990, from homes without smokers was enrolled. The daily occurrences of respiratory symptoms and breastfeeding status were reported by the mothers every 2 weeks. Illnesses were classified as lower respiratory illness (LRI) if wheezing or wet cough was reported; the remaining illnesses were classified as upper respiratory. The annualized incidence rates for LRI were 2.8, 2.6, and 2.1 during follow-up time with no, partial, or full breastfeeding, respectively, but the incidence rates for upper respiratory illness and lower respiratory illness combined were similar in the three categories. After adjustment for potential confounding factors, full breastfeeding was associated with a reduction in lower respiratory illness risk (odds ratio=0.81, 95% confidence interval 0.68-0.96). Median duration of all respiratory illnesses was 5 days for the fully breastfed infants during the first 6 months of life compared with a median of 6 days for not breastfed and partially breastfed infants. Multivariate analysis confirmed that breastfeeding significantly reduced the duration of respiratory illness. This pattern of reduced incidence of LRI and shorter duration of all respiratory illnesses suggests that breastfeeding reduces the severity of infant respiratory illnesses during the first 6 months of life.

Background:Women are at substantially greater risk for anterior cruciate ligament (ACL) injuries than are men.Purpose:To conduct a systematic review and meta-analysis of the literature to clarify the effect of the menstrual cycle and contraceptives on the laxity of and noncontact injuries to the ACL.Study Design:Systematic review; Level of evidence, 4.Methods:Searches were conducted using MEDLINE (1946–August 2016), the Cochrane Library Database, clinical trial registries, and related reference lists. Search terms included athletic injuries, knee injuries, ligaments, joint instability, menstrual cycle, ovulation, hormones, and contraceptives. Investigators independently dually abstracted and reviewed study details and quality using predefined criteria and evaluated overall strength of evidence using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) criteria.Results:Twenty-one studies totaling 68,758 participants were included: 5 on the menstrual cycle and ACL injury, 7 on hormonal contraceptives and ACL injury, as well as 13 on menstrual cycle and ligament laxity. Four of 5 studies of women not using hormonal contraception indicated that the luteal phase was the least associated with ACL injuries. The 2 largest and highest quality studies on hormonal contraceptives suggested that hormonal contraceptives may be protective against ACL injury. Six of 12 studies on ACL laxity provided quantitative data for meta-analysis, finding significantly increased laxity during the ovulatory phase compared with the follicular phase.Conclusion:The literature suggests an association between hormonal fluctuations and ACL injury. Recent studies have suggested that oral contraceptives may offer up to a 20% reduction in risk of injury. The literature on ACL injuries and the menstrual cycle has more than doubled over the past decade, permitting quantitative analysis for the first time. However, the overall strength of this evidence is low. Promising potential directions for future research include long-term observational studies with ongoing hormonal assays and large interventional trials of follicular suppression, including newer hormonal methods.

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