Osteoporosis is related to a variety of genetic factors and environmental factors. eggs intake is a correctable environmental factor, which may represent a potentially low-cost prevention strategy. This study was aimed to investigate the possible association between eggs intake and osteoporosis, VF in 673 40-74-year-old participating in the CBLAST. An independent association of regular intake of eggs with a lower risk of osteoporosis was observed. A separate analysis of male and female subjects didn’t substantively change the results even after adjustment for confounding factors. While no significant correlation was observed between eggs intake and VF in our data.
Our results demonstrated that participants who consumed eggs daily had higher trabecular volumetric BMDs derived from QCT (96.8 mg/cm3 vs. 79.3 mg/cm3, p = 0.002) and lower prevalence of osteoporosis (27.2% vs. 54.1%, p < 0.001) compared with participants who didn’t. We also observed that subjects who consumed eggs regularly were also more likely to consume other foods or drinks regularly, such as vegetables, fruits, meat, and yogurt which play recognized or possible roles in bone health[8]. After adjusting for dietary and other confounding factors, the association between eggs intake and osteoporosis was still statistically significant. Although relatively limited investigations have studied the role of eggs consumption in bone outcomes, eggs were respect to have beneficial effects on bone strength in most of the prior studies[11–13]. In a longitudinal study, Inose et al. used a composite measure of dairy products and eggs, the total scores of which were positively correlated with Z-scores for tibia cortical speed of sound, a measure associated with cortical strength, in the first graders' mothers with a median age of 37.8 years old[11]. Rodopaios and colleagues also indicated that BMD and bone mineral content (BMC) were positively, though weakly, correlated with poultry and eggs consumption in 400 fasters and non-fasters[12]. The only study that investigated the association between eggs intake and bone strength in isolation was conducted in 294 healthy children aged 9–13 years old[13]. They showed that egg intake was a positive predictor of mid-radius cortical bone mineral content (BMC) and may represent a viable strategy to promote pediatric bone development. In addition, a meta-analysis, which included 55 case-control studies on the relationship between dietary factors and lung cancer, showed that eggs intake is one of the protective factors of lung cancer[14]. Considering the possible role of eggs on prevent osteoporosis and lung cancer, one-stop screening for lung cancer and osteoporosis may be more meaningful to people who consume eggs less than once a day.
It should be noticed that eggs intake was not significantly associated with the risk of VF among all subjects and also subgroups by sex in our data no matter covariates were adjusted or not (all P > 0.05). To our knowledge, there are no prior studies examining the relationships between egg consumption and VF. Similarly, the risk of hip fracture was found to have no association with total poultry or egg consumption in elderly Chinese[15]. The reason might be that in addition to bone strength, fractures are also affected by other complex factors such as fall-related factors[16]. Although the proportion of VF in the osteoporosis group is significantly higher than that in the non- osteoporosis group, more than 50% of the participants with VF didn’t have osteoporosis in the entire population as well as in the male and female subgroup in the present study (shown Table 4). Randomized controlled trials are required on the association between eggs intake and fractures including more fracture-related factors in the analysis.
The benefit of eggs intake on bone health could be related to the protein which plays an important role in bone formation. Protein intake influences the production of insulin-like growth factor-1 which not only has growth-promoting effects on bone but also stimulated the uptake of calcium and phosphate[17]. In a meta-analysis, moderate evidence suggested that higher protein intake was associated with a 0.52% (95% CI: 0.06% − 0.97%) increase in lumbar spine BMD compared with lower protein intake[18]. Recent studies have also investigated the association between fracture and dietary protein intake in the elderly[19, 20]. However, a systematic review and meta-analysis over 40 years found little benefit of increasing protein intake for bone health in healthy adults but no indication of any detrimental effect, at least within the protein intakes of the populations studied (around 0.8-1.3g/Kg/day)[21]. In addition, eggs are high-quality sources of vitamin D, zinc, and bioactive peptides that may benefit bone health. There is consensus that vitamin D supplementation can prevent and cure nutritional rickets in infants and children[22]. Although the skeletal effects of vitamin D deficiency in adults and older adults are controversial, most guidelines recommend serum 25-hydroxyvitamin D concentrations of > 50 nmol/l for optimal bone health in older adults[23]. A randomized controlled trial supporting the role of zinc supplementation for increasing procollagen type 1 amino-terminal propeptide, a bone formation marker, in premenarcheal girls[24]. Eggs are also recognized as a functional food that contains a variety of bioactive compounds that can influence pro- and anti-inflammatory pathways such as phospholipids, cholesterol, the carotenoids lutein and zeaxanthin, and egg white- and yolk-derived proteins[25]. These bioactive components may mediate a potential benefit on bone geometry by protecting against inflammation-induced bone loss[25–27]. For example, egg yolk-derived peptide dose-dependently increased MG-63 cell proliferation, ALP activity, collagen synthesis, and calcium deposition by affecting osteogenic gene expression[28].
Eggs not only have a direct effect on the bone health but also indirectly affect bone through actions on skeletal muscle. There was evidence showing that skeletal muscle can affect bone homeostasis in mechanical and non-mechanical fashion and is a strong positive predictor of bone mass[29, 30]. In Chinese community-dwelling middle-aged and elderly men, whole body BMDs except skull BMD were also found to be positively correlated with appendicular skeletal muscle mass[31]. The anabolic effect of protein ingestion on stimulating muscle protein synthesis has been well-reported[32, 33], while few studies investigated the effects of eggs intake on muscle. In the univariate analysis, meat intake was statistically different from osteoporosis, which may also be the reason. The significant positive relationships between eggs intake and fat-free soft tissue mass were only reported in healthy children[13]. It is unclear whether eggs intake strength skeletal muscle in middle-aged and elderly people and need further research.
This study has some strengths. Firstly, the present study is the first study investigating the possible associations of eggs intake with osteoporosis and VF independent of other diets in middle and elderly people. These findings help to understand the effect of whole eggs not single nutrients on bone health. Secondly, Asynchronous QCT was used to measure BMD derived from chest LDCT scans without additional radiation exposure. Our study provides evidence for optimizing the target population of opportunistic osteoporosis screening and formulating a more personalized screening plan.
There are also some limitations in this study: First, due to the cross-sectional study design, causality can’t be inferred between eggs intake and osteoporosis, VF. Second, our findings can only be generalized to middle-aged and elderly Chinese. Thirdly, although the doctors who conducted the questionnaires were uniformly trained, self-reported dietary intake is subject to error as it depends on memory and is susceptible to under or over-reporting. Given we used data from the CBLAST which was not originally intended to assess eggs intake, the number of eggs intake was not recorded and needs further studies. Finally, the analyses were adjusted for the majority of confounding factors, but the possibility of residual confounding bias due to unknown or unmeasured covariates cannot be entirely ruled out.
In conclusion, the present study suggests an association between daily eggs intake and lower risk of osteoporosis, but not VF, in middle-aged and elderly Chinese. Opportunistic osteoporosis screening may be more meaningful to people who consume eggs less than once a day, and daily eggs intake could have a significant public health impact if the positive influence of eggs on bone health is confirmed through future randomized controlled trials.