Osteoarthritis Causes and Risk Factors
Osteoarthritis (OA) arises as a result of a complex interplay of factors such as aging, mechanical forces, joint integrity, local inflammation, genetics, and congenital abnormalities (Kalunian 2012a; Bijlsma 2011).
Risk factors for osteoarthritis include (Seed 2011; Busija 2010):
- Advanced age
- Female gender
- Obesity (see below)
- History of physical labor
- High-impact sports
- Joint trauma
- Family history
Obesity and Osteoarthritis
Because obesity increases the load and stress on many joints, it appears to be one of the most influential risk factors contributing to the development or advancement of osteoarthritis (OA) (Busija 2010). However, studies of obese patients have identified a high prevalence of OA in non-weight bearing areas (e.g., finger joints) as well (Rai 2011).
Data reveal that fat tissue is a major source of catabolic and pro-inflammatory mediators (i.e., cytokines, chemokines, and adipokines), which are implicated in the process of OA (Rai 2011). In addition, obese patients tend to experience insulin resistance and increased glucose load, which may also contribute to the chronic inflammation and cartilage degradation of OA (Sowers 2010).
Since OA has been linked not only to obesity, but also to other cardiovascular risk factors (e.g., diabetes, dyslipidemia, hypertension, and insulin resistance), researchers have proposed that it might be related to a much larger group of risk factors, called “metabolic syndrome” (Velasquez 2010; Katz 2010).
Recent studies have shown that physical activity and diet programs (alone or in combination) are associated with a reduction in pain, as well as functional improvement among overweight or obese adults with OA (Brosseau 2011). In cases where patients are too obese to engage in physical activity, bariatric surgery has also been correlated with improvements in pain and function among patients with OA of the hip and knee (Gill 2011).
Metabolic Factors Associated with Osteoarthritis
Several interrelated metabolic factors also contribute to osteoarthritis onset and progression; chief among which are inflammation, mitochondrial dysfunction, and oxidative stress.
Inflammation – Osteoarthritis (OA), like many other age-related diseases, is tied to excessive inflammation (Goldring 2011).
Over-indulgence in foods rich in pro-inflammatory omega-6 fatty acids and insufficient intake of foods rich in anti-inflammatory omega-3 fatty acids characterizes the dietary pattern of most modern, industrialized nations.
Arachidonic acid (an omega-6 fatty acid) is the raw material used by the body to synthesize numerous inflammatory mediators, including leukotriene B4, prostaglandin E2, and thromboxane A2, all of which contribute to pain, swelling, and joint destruction (see figure 1) (Liagre 2002; Devillier 2001; Kawakami 2001).
Mitochondrial dysfunction – Mitochondria are the power cores of our cells; they generate the energy that cells need to function. With age, mitochondrial function deteriorates, leading to a variety of negative consequences (Vaamonde-Garcia 2012; Cillero-Pastor 2008; Blanco 2004).
In the case of OA, dysfunctional mitochondria conspire with inflammation to augment joint destruction. One study found that the inflammatory propensity of chondrocytes was amplified when their mitochondria were dysfunctional. Specifically, mitochondrial dysfunction in chondrocytes is associated with increased reactive oxygen species production and activation of the “master-regulator” of inflammation, nuclear factor-kappa B (Nf-kB) (Vaamonde-Garcia 2012).
Fortunately, adhering to a plant-based diet rich in dietary antioxidants, reduced in saturated fat, and balanced in omega-6 and omega-3 fats, such as the Mediterranean diet (see Nutritional Interventions section below) may be an effective means of targeting several of the metabolic imbalances that affect OA.
Oxidative stress - Oxidative stress, which is caused by free radicals, is known to be a factor in cartilage destruction and inflammation. These reactive molecules are also involved in pain perception (Ziskoven 2010).
(Aldamiz-Echevarria 2007; Wixted 2010; Simopoulos 2011; Schror 2011; Bengmark 2006; Murias 2004; Oz 2008; Keicher 1995; Prasad 2004; Safayhi 1992)