Parity, Lactation, and Fracture Risk: What’s the Link?

Parity and lactation had a neutral effect on the risk for fragility fractures or radiographic vertebral compression fractures over 10 years of follow-up.

Parity and lactation showed no significant associations with osteoporotic fragility fractures or radiographic vertebral compression fractures over 10 to 16 years of follow-up, according to study results published in Archives of Osteoporosis.

Prior research studies examining the effect of reproductive variables such as parity and lactation on osteoporosis and fractures have largely been retrospective and small. Researchers conducted a multicenter randomly recruited population-based cohort study that consisted of women who participated in the Canadian Multicentre Osteoporosis Study, which began in 1995. All members of the study cohort were eligible for inclusion in the analysis (N = 6539). Investigators analyzed 16 years of prospective incident clinical fracture data, 10 years of radiographic vertebral fracture data, and 10 years of data measuring change in areal bone mineral density (aBMD) to determine whether parity or lactation affect bone mineralization or fracture risk.

Study participants were asked to complete a standardized study questionnaire administered by an interviewer that assessed lifestyle variables, nutrition, demographics, general health, and medical history.

The primary outcome was any clinical fragility fracture after 16 years of follow-up at 6 skeletal sites: ribs, spine, forearm, hip, shoulder, and pelvis. The secondary outcomes were a radiographic vertebral compression fracture over 10 years and change in aBMD over 10 years at the lumbar spine, total hip, and femoral neck.

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Over 16 years of follow-up in 3437 women, 633 (18.4%) experienced ≥1 clinical fragility fractures. Over 10 years of follow-up in 3839 women who had full evaluable radiograph data, only 98 (2.6%) experienced ≥1 incident deformity or fracture. Neither analysis showed significant associations with lactation or parity.

There were also no significant associations between aBMD and lactation at the 3 skeletal sites over 10 years. For each live birth, parity was linked to a slightly adverse decline in aBMD of the femoral neck, but had no association with aBMD change of the total hip or lumbar spine. Of note, there were no associations between lactation and change in aBMD of the spine, where the greatest changes in microarchitecture and aBMD take place.

Reported study limitations included potential recall bias, majority white population, and relatively small number of women who breastfed for a prolonged duration, with the mean lifetime duration of breastfeeding being 12 months in women in the study who lactated.

Researchers noted that “[t]hese randomly obtained, population-based data provide strong reassurance that two common and positive reproductive experiences for women do not have negative long-term effects on the risks of developing fragility fractures or a more rapid decline in aBMD.”

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Cooke-Hubley S, Gao Z, Mugford G, et al. Parity and lactation are not associated with incident fragility fractures or radiographic vertebral fractures over 16 years of follow-up: Canadian Multicentre Osteoporosis Study (CaMos). Arch Osteoporos. 2019;14:49.