Older Adult Bone Health Linked to Breast Milk in Infancy

Written by: Lauren Milligan Newmark, Ph.D. | Issue # 96 | 2020

Older adults looking to keep their bones strong might turn to a glass of milk with lunch to help meet their daily calcium and vitamin D requirements. New research [1] suggests that older adults interested in healthy bones might also want to find out what they drank for lunch as an infant.

Despite the 70-year gap, there are good reasons to believe that infant feeding practices are connected to bone health in later life. Differences in infant feeding practices (i.e. breast milk or formula) have been linked to body length and growth rates both during the first year of life and later in childhood [2, 3]. Early growth rates, in turn, are related to the density of the skeleton when it reaches peak bone mass during the third decade of life [3, 4]. And how strong and dense your bones are at their peak can predict how they will hold up once resorption (or bone loss) exceeds bone formation [4].

But testing these life history connections is tricky, requiring data collected more than a half century apart. A new study took advantage of the unique data set available from the Hertfordshire Cohort Study (HCS), which included almost 1000 males and females born between 1931 and 1939 in Hertfordshire County, Great Britain. All cohort members had health visitor ledgers from their first year of life that included data on birth weight, weight at 1 year, and whether the individual was breast milk fed, breast and bottle milk fed, or bottle fed during the first year and were still living in Hertfordshire County between 1998 and 2004 and available for bone density testing [1]. The data are not ideal, as collections in the 1930s were not performed with any knowledge of how the information would be used decades later. But even without data on age at first solids or age at complete weaning, the HCS still allows researchers to test the hypothesis that infant nutrition is a potential mediator of adult bone health [1].

All participants (498 males and 498 females, who were on average 65 years old) completed questionnaires at the time of their bone scans about potential confounding variables including smoking, exercise, alcohol consumption, diet, and (for females) use of hormone replacement therapy. Dietary information was converted to a prudent diet score as a marker of dietary quality and also used to calculate daily dairy intake. Finally, each participant had his or her lumbar spine and femoral neck scanned for bone mineral content (BMC, or how much bone mineral in grams is in a specific area) and bone mineral density (BMC divided by the area of the bone, or grams/square centimeter) by dual-energy X-ray absorptiometry (DXA). Each participant was separated into either the breast-fed group, meaning no milk other than mother’s milk was provided for the first year of life, or bottle-fed, which included those that were bottle fed and those that received both bottles and breast milk. Using historical records, the study authors determined that bottles were most likely filled with cow’s milk preparations rather than commercial infant formula, which was not widely used during the 1930s in Great Britain [1].

Infant feeding was found to be a significant predictor of bone health in later life, but only in males [1]. After controlling for all confounding variables, bottle-fed males had significantly lower lumber bone mineral density (BMD) measurements than those that were breast fed. But what about females? The study authors propose that for females, factors such as hormones, age at menopause, and postmenopausal lifestyle (weight-bearing exercise, diet) may have a stronger influence on bone density during later life and override any potential effects from infant diet [1].

Normally, this is the part of the article where the results of this study would be discussed in the broader context of research on breast milk during infancy and bone health later in life. Unfortunately, the unique aspects of the HCS population make such discussions challenging. For starters, a review paper on infant milk feeding and bone mass reported that whether or not breast milk and BMD were positively associated depended on the age of study participants [5]. With no other studies on 60 and 70 year olds, the HCS lacks an age-matched population. But equally challenging is the fact that the HCS also lacks a diet-matched population; all other studies on infant diet and bone health examine the influence of breast milk or commercial infant formula, not cow’s milk. The suggestion that breastfeeding may potentially provide a protective effect on bone health in males as they age must therefore be interpreted with caution. It is certainly intriguing, however, to think of breast milk conferring health benefits far beyond infancy, even into the twilight years.

References

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