Health Matters

Osteoarthritis - Is excess weight really a cause?

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What do know about OA? First, medicine considers it ‘idiopathic i.e. ‘no specific cause’, and different from trauma induced OA. Young people can suffer from it, prevalence increases significantly with age. Comorbidities are common e.g. hypertension, obesity, diabetes, COPD, CAD and stroke, disorders heavily influenced by diet / life-style. Patients with previous hand OA have increased likelihood of incident knee and hip OA (independent of weight). Such facts support a systemic (think diet/lifestyle) cause for idiopathic OA. Yet:

  1. excess weight and
  2. repetitive tasks (kneeling, squatting heavy lifting)

are commonly listed as key causes of OA development.

Let’s consider the following. The amount of weight carried by joints is ordered: ankle > knee > hip. Taken at face value, this would suggest that occurrence of OA should be lowest in hips, more frequent in knees and greatest in ankles. In line with this, hip OA makes up around 19% of cases, knee OA 41%, yet ankle OA bucks the theory and is unexpectedly rare, about 4% of OA cases and weight doesn’t explain why 30% of OA cases involve the hands.

Research at Duke University medical school shows that the weight carried by each joint does affect joint function, but in a very surprising way. It turns out that when a joint carries more weight the body compensates for the increased load on cartilage by increasing a thing called cartilage ‘protein turnover’. The concept is actually quite simple. Protein turnover is the rate at which new fully functional proteins are synthesised to replace older worn-out proteins, which are broken down. The faster this occurs the more, new proteins you have and the stronger your cartilage. If fact, protein turnover is a de facto marker for a tissue’s ability to be able to repair itself and protein turnover increases from hips to knees to ankles so that each joint can handle its extra load.

Given all of the above, it’s much more likely that OA just develops along with (but not because of) obesity. In this model, obesity and OA (along with the other comorbidities listed above) likely develop as a result of metabolic derangements, eventually caused by poor diet/lifestyle.

But why so much knee OA? Some studies do not differentiate between OA caused by previous trauma and idiopathic OA. Importantly previous traumatic knee and ankle injuries increase the relative prevalence of both knee and ankle OA. Indeed, traumatic injury is one of the strongest risk factors for subsequent OA. The knee just happens to be relatively unprotected by surrounding tissue and the most easily and commonly injured joint. So traumatic knee injury (but not including simple wear & tear) contributes to the overall increased prevalence of all cause OA in this joint. Differentiating non-traumatic OA is important because, without traumatic injury idiopathic OA is, ironically, much more likely to occur among sedentary individuals. So, first eat right, then exercise regularly by doing both cardio & strength work, keep your joints strong and so lose a little weight! Just be more careful and don’t get yourself a major joint injury.

 

Article Written + Submitted by:

Andreas Klein Nutritionist + Remedial Therapist from Beautiful Health + Wellness
P: 0418 166 269

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