Bone health begins in childhood, particularly during the rapid bone accrual phase of puberty, which is essential for attaining optimal peak bone mass. Peak bone mass is achieved in early adult life and affects both immediate and future fracture risk. Genetic, nutritional, exercise-related, and hormonal factors, and certain diseases and medications, have deleterious effects on bone health.

In addition, emerging data suggest that certain manmade chemicals known as per- and polyfluoroalkyl substances (PFAS) may affect bone accrual during this important period and potentially increase the risk for osteoporosis in adulthood. Osteoporosis refers to increased fracture risk because of low bone density and affects a large proportion of postmenopausal women and older men.

New evidence comes from a recent study conducted by investigators from the Keck School of Medicine , who examined the impact of exposure to PFAS on skeletal outcomes in youth. Of note, participants were primarily Hispanic; this population has a higher risk for osteoporosis in adulthood. PFAS are manmade chemicals with water- and grease-resistant properties. They are used in a variety of products, such as nonstick cookware, food packaging, water-repellent clothing, stain-resistant fabrics, carpets, and in certain industrial processes. They are pervasive in the environment, in wildlife, and in humans.

Use and production of certain PFAS, such as perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA),  have decreased over the past two decades, with a significant reduction in blood concentrations of these chemicals. However, they can be resistant to degradation and have very long half-lives. As a consequence, these “forever chemicals” continue to linger in the environment. Also, the risk for exposure to other PFAS persists, and almost every individual has detectable levels of PFAS in blood.

Scientists are still learning about the impact of environmental chemicals on bone health. In contrast, other factors that may jeopardize pubertal bone accrual and peak bone mass acquisition have been studied extensively, with guidelines for management of the consequent poor skeletal health.

For PFAS, studies have reported deleterious effects on various body systems, such as the liver, immune system, thyroid, and the developing brain. The limited data related to bone suggest negative associations between certain, but not all, PFAS and bone density — ie, the higher the exposure, the worse the impact on bone health.

PFAS may affect health through alterations in the endocrine system. They have been associated with lower levels of testosterone and downregulation of its receptor (and testosterone is known to modulate bone formation and bone loss). On the other hand, some PFAS are estrogenic, which should be beneficial to bone. A direct impact of PFAS on pathways regulating activity of osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells) has also been postulated, with conflicting results.

Previous research on PFAS and human bone health has found mixed results. In adolescents, Xiong and colleagues  reported negative associations of PFOS, PFOA, and perfluorononanoic acid (PFNA), but not perfluorohexane sulfonic acid (PFHxS), levels with bone density at various sites, mostly in females. Carwile and associates  reported similar negative associations of blood concentrations of PFOA and PFOS and urinary concentrations of phthalates with bone density in adolescents, but only in males. Lin and coworkers also reported negative associations of PFOA and bone density in adult premenopausal women, but found no associations of PFOA and PFOS concentrations with self-reported fractures, suggesting questionable biological significance of these findings. These were all cross-sectional studies and did not report on the impact of these chemicals on longitudinal bone accrual.

In the recent study, Beglarian and colleagues examined the impact of PFAS on longitudinal changes in bone density in adolescents, drawn from the Study of Latino Adolescents at Risk of Type 2 Diabetes (SOLAR) cohort and young adults from the Southern California Children’s Health Study (CHS) cohort. They found that in adolescents, higher baseline concentrations of PFOS predicted lower bone accrual over time. In young adults, there was a similar negative association of PFOS concentrations and bone density at baseline, but not with longitudinal bone accrual. In this study, other PFAS were not associated with bone outcomes.

Overall, research appears to suggest that PFOA, PFOS, and PFNA may have deleterious effects on bone density and bone accrual over time. However, data are not consistent across studies and across sexes, and more research is necessary to conclusively define the impact of these chemicals on skeletal health, particularly during the critical pubertal years of maximal bone accrual. In the meantime, continued efforts are necessary to reduce to concentrations of these PFAS in the environment.