Meteorological variables and the risk of fractures: A systematic review and meta-analysis

Highlights

• First meta-analysis to examine the association between temperature, humidity, and other meteorological factors and fractures.

• Temperature decrease increases fracture risk and current studies don’t support the positive link for relative humidity.

• A significant association was found for freezing rain, snow, but not for RH, dew, frost, fog, storm and high wind.

• It is more effective to measure the association between temperature decrease and fracture risk on a daily time scale.

• Populations in Asia, subtropical zone, low-latitude, and northern hemisphere are vulnerable to temperature decrease.

Abstract

Purpose

The association between meteorological variables and risk of fractures has attracted increasing attentions but remain controversial. Therefore, our main aim is to clarify the association, and also to identify possible susceptible groups.

Methods

Relevant literature was obtained through standard MeSH literature searching seven electronic databases. Because some studies expressed the association as the rate of incidence (IRR) of fractures associated with each 1 °C rise in temperature and 1% increase in relative humidity (RH), some expressed as IRR of fractures for the day with specific climatic variable versus control days, and also the association was expressed as correlations coefficients (COR) in some studies, separated meta-analyses were undertaken, with one based on IRR and another based on COR.

Results

A total of 24 studies were included. Results showed that each 1 °C increase was significantly associated with a 3.0% decrease in fracture risk (IRR = 0.970, 95%CI: 0.952–0.988). The day with freezing rain and snow were associated with increased risk for both the lower extremity fracture (freezing rain: IRR = 1.174, 95%CI: 1.022–1.348; snow: IRR = 1.245, 95%CI: 1.050–1.477) and the upper extremity fracture (freezing rain: IRR = 1.376, 95%CI: 1.192–1.588; snow: IRR = 1.548, 95%CI: 1.361–1.761). No significant association was detected between RH, dew, frost, fog, storm and high wind, and fracture. The COR meta-analysis showed that mean temperature (moderately), maximum temperature (moderately), rainfall (weakly) and sunlight duration (weakly) were correlated with fracture occurrence.

Conclusion

The incidence of fractures was increased in lower temperature, the day with freezing rain, and snow. Other meteorological factors may have some effects on the incidence of fracture. The association maybe stronger for males, lower extremity fracture, and people living in Asia, subtropical zone, low-latitude, and northern hemisphere. Further studies are needed.

Introduction

Fractures become increasingly common in elderly, resulting in substantial bone-associated morbidities, loss of independence, lasting disability, and increased mortality and health-care costs (Sanders et al., 1999; Shauver et al., 2011). Osteoporotic fractures and fragility fractures are the two most common types of fracture. Osteoporosis is defined as a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture (Conference, 1993). Fragility fractures are caused by low-energy trauma (slips, trips, and falls from standing height) (Dare and Hu, 2017). Roughly 9 million osteoporotic or fragility fractures occur worldwide per year (Johnell and Kanis, 2006). Annual costs associated with fragility fractures exceed €36 billion in Europe (Burge et al., 2007). In the USA, there were 2 million incident osteoporotic fractures that cost approximately $17 billion in 2005, and 3 million incident fractures and a cost of $25 billion are expected by 2025 (Burge et al., 2007). In addition, the mortality at 1 year after fracture is about 10% - 20% (Leibson et al., 2002) with only 40% regaining full pre-fracture independence (Li et al., 2014). Worldwide, people older than 65 years was around 506 million in 2008, and by 2040 this number is expected to increase to 1.3 billion (Kinsella and He, 2009). Given the rapid aging of the world's population, the number of fractures and associated costs are projected to increase by two to four times worldwide in the next few decades (Briggs et al., 2016).

There are many risk factors contributing to the occurrence of fractures, including decreased bone mineral density (BMD), low vitamin D levels, lower limb strength, sensory system function (vision, vestibular, and proprioception), flexibility, and postural balance decline (Low Choy et al., 2007; Melton et al., 2010; Jang et al., 2012; Louer et al., 2016). However, the role of climate in the incidence of fracture has received much less attention, so its real impact has yet to be fully elucidated. Recently, emerging studies (Jacobsen et al., 1995; Levy et al., 1998; Jacobsen et al., 1999; Lin and Xiraxagar, 2006; Bischoff-Ferrari et al., 2007; Tenías et al., 2009; Lau et al., 2010; Turner et al., 2010; Leavy et al., 2013; Giladi et al., 2014; van den Brand et al., 2014; Tenías et al., 2015; Al-Azzani et al., 2016; Fraenkel et al., 2017; Mazzucchelli et al., 2018; Lofthus et al., 2001; Mirchandani et al., 2005; Murray et al., 2011; Modarres et al., 2012; Modarres et al., 2014; Koren et al., 2014; Jo et al., 2018; Segal et al., 2018; Warrender et al., 2018) have focused on the influence of meteorological factors on the incidence of fractures, especially temperature, relative humidity (RH), freezing rain, and snow, but the results are inconsistent. The fracture types varied in these studies, among which hip fractures (HFs), distal forearm fractures (DFFs), and distal radius fractures (DRFs) were dominantly and contribute significantly to the burden of fractures. For instance, Tenías et al. (2009) found that higher temperature was associated with higher fracture incidence. But Bischoff-Ferrari et al. (2007) reported that higher winter temperatures were inversely related to the risk for DRFs and ankle fractures. As for freezing rain the main result of previous studies is that the day with freezing rain is associated with a higher although some were not statistically significant incidence of fractures (Levy et al., 1998; Jacobsen et al., 1999; Giladi et al., 2014), but contrary results also exist (Jacobsen et al., 1995). For snow, the results of previous studies are the same as freezing rain (Jacobsen et al., 1995; Jacobsen et al., 1999; Leavy et al., 2013; Giladi et al., 2014; van den Brand et al., 2014; Al-Azzani et al., 2016; Mazzucchelli et al., 2018). For other meteorological variables (e.g. rainfall, RH, sunlight duration, dew, frost, fog, storm, high wind, and temperature ≦ 0 °C) inconsistent results also existed.

As fractures require a multidisciplinary treatment approach, ranging from surgery to physiotherapy and rehabilitation, thus, the identification of the risk factors for fractures, including meteorological variables, is critical to the development of effective preventive programs and healthcare resources planning. Although there are emerging studies exploring the relationship between meteorological factors and fractures, the focused meteorological factors and conclusions of each study are different. Therefore, we conducted this meta-analysis of previous findings with the main aim to explore the association, to quantify the size of the effects, and to identify the vulnerable populations for prevention.