Our results revealed that higher DII, indicating of more pro-inflammatory diets, were associated with higher osteoporosis risk in women at the baseline, while no association was found in men. Increased DII was associated with lower lumbar spine, total hip and femoral neck BMD in women. While in men, there was a negatively association between DII and BMD in lumar spine only.
A number of studies have indicated that diet, as the key source of biologically active ingredients, could mediate inflammation response [23]. A previous study also found that the diet with high inflammatory potential was significantly associated with an increased risk of osteoporosis in women, but not in men [6]. This is consistent with our findings. However, another study in China reported that a pro-inflammatory diet was associated with a higher risk of osteoporotic hip fracture in both men and women [24].There may be some reasons, on the one hand, perhaps it was mainly because the incidence of men with osteoporosis was far lower than that of women (among the 2206 individuals who developed osteoporosis, only 40 were men and 164 were women). On the other hand, due to the effects of the sex hormone and the genetic differences between men and women, it was common for women to take the leading role in the autoimmune diseases such as osteoporosis, which could explain the overall sex difference in the rate of incident osteoporosis [6][25, 26]. Therefore, further investigations are needed to clarify the association between DII and the risk of osteoporosis in men. In addition, as far as we know, many studies have investigated the relationship between DII and BMD. A study indicated that increasing DII scores were significantly associated with decreases in lumbar spine and total hip BMD in both men and women [27]. Another study among Iranian postmenopausal women showed that less DII scores were associated with significantly higher BMD of the lumbar spine and a non-significantly higher BMD of the femoral neck [28]. This may be due to the fact that the relationship between BMD and DII varies by race, age, gender, and the site of BMD measurement [7].
There was no association between DII and osteopenia in our study. There may be some reasons: 1) It may be due to the uncertainty of dietary intake. Such as, it was reported that moderate drinking was beneficial to the health of the bones of the elderly or had a neutral impact, but long-term excessive drinking would lead to bone loss and osteoporosis [29]. 2) In addition to diets, aging, genetics and other hormonal factors also play a crucial role in bone mass regulation and preservation [30]. In subgroup analysis of age stratification, DII was positively correlated with osteoporosis in women. However, after adjusting for all confounders, the OR of those younger than 65 years old was higher than that of those older than 65 years old. This may be due to rapid bone loss in the first few years of post-menopause [31]. In the analyses of BMI stratification, we found that DII was positively linked with osteoporosis in women when BMI < 25. According to the previous study, A BMI of 25 kg/m2 was identified as the reference point, below which, the risk of hip and any bone osteoporotic began to increase [32].
Proinflammatory diets could lead to poor bone health through several mechanisms [18].For instance, the effect of pro-inflammatory diet on osteoclast activity increases systemic inflammation [33]. IL-1 and IL-6 have uncoupled bone remodeling by enhancing bone resorption and suppressing bone formation [34]. Inflammatory cytokines directly mediate bone loss by stimulating the formation and maturation of osteoclast or indirectly by promoting the release of ligand-RANKL [35].
Previous studies have mostly focused on the relationship between specific nutrients or dietary pattern and the risk of osteoporosis or BMD. It was reported that intake of red meat and butter might increase the concentration of CRP, E-selectin, and soluble vascular cell adhesion molecule, reflecting rising systemic inflammation [23]. Another study of 3,236 Scottish women aged 50 to 59 found that eating more fruits and vegetables might reduce bone loss and dietary patterns rich in processed foods were linked with reduced BMD [36]. These studies may have some limitations. On the one hand, the real effects of the food or nutrient may be weakened or aggravated because of dietary correlations [28]. On the other hand, adherence to a specific diet pattern may not be a practical choice for most people due to differences in dietary culture and availability [37]. DII considers the full spectrum of food ingredients that regulate inflammation. It more accurately reflects the relationship between diet and BMD than individual nutrients [28]. In addition, it is more reliable to assess the quantitative relationship between diet quality and osteoporosis, rather than dietary patterns ,which are not quantitative [38].
There were some limitations to this study. First, the causality deduction between DII and BMD was limited, because it was a cross-sectional study. Second, even if BMD represented the accumulation of bone changes that reflected long-term diet exposure for many years, the DII was calculated using 24-h recalls data. Third, due to the differences between the individual being included and excluded, there might be potential selection bias. Fourth, there were too few cases of osteoporosis in men to make precise conclusions. Despite these limitations, this study has several strengths. First, our data were adjusted for several demographic factors, lifestyles, and dietary factors as confounders. Second, the data sample in this study was based on a nationally representative random sample of the general population of US, so we could extrapolate our results to the general population.
In conclusion, diets with higher inflammatory potentials were significantly associated with increased risk of osteoporosis in women, though not significantly in men. Increased DII was associated with lower lumbar, total hip, and femoral neck BMD in women. In men, however, DII was only negatively correlated with BMD in the lumar spine. Therefore, the intake of foods with less inflammation to prevent osteoporosis has become increasingly important.