Systemic and dietary risk factors for knee osteoarthritis. Association of serum vitamin D, metabolic syndrome, dietary magnesium intake and serum C-reactive protein with the risk of knee osteoarthritis.

Knee osteoarthritis is a common cause of knee pain and loss of function especially in older age groups. In Finland, in the Health 2000 Survey, 6% of men and 8% of women had prevalent knee osteoarthritis. The disease’s course is chronic and progressive, and no curative treatment options are currently known.

Knee osteoarthritis has shown to have several load-based risk factors, such as overweight, work-related loading factors and knee malalignment. Of the systemic knee osteoarthritis risk factors, most evidence exists on female gender and genetic factors. There is growing interest in potential systemic risk factors of knee osteoarthritis, such as low serum vitamin D levels, metabolic syndrome and its components, low-grade systemic inflammatory state, and low dietary magnesium intake.

Many aspects in the results of previous studies have been conflicting. In the original studies of the compilation thesis, none of the studied potential risk factors were associated with an increased risk of incident knee osteoarthritis. The objective of this thesis was to examine the potential systemic risk factors of knee osteoarthritis. For this prospective cohort study, patient data were obtained from the nationally representative Mini-Finland health survey and Health 2000 survey databases. Follow-up data on incident knee osteoarthritis cases were obtained from the national Care Register for Health Care database. The follow-up periods of the original studies were long, 10-32 years.

None of the studied potential risk factors – low serum vitamin D level, metabolic syndrome or its individual components, serum high sensitivity C-reactive protein or lower dietary magnesium intake – were associated with an increased risk of developing knee osteoarthritis. Instead, elevated fasting plasma glucose levels seemed to decrease the risk of incident knee osteoarthritis. We also found that season of blood draw seems to be a significant effect modifier on the association of serum vitamin D level and the risk of knee osteoarthritis, which merits attention in future studies.

Given the chronic nature of the disease and the lack of curative treatment methods, better understanding of the pathogenesis and risk factors of knee osteoarthritis are needed, as well as knowledge of preventive methods. To obtain this, further studies with large study populations, long follow-up periods, repeated measurements of the potential risk factors and the use of modern diagnostic criteria with both clinical and radiographic criteria are needed.

The thesis provided information on the role of systemic factors in the risk of knee osteoarthritis. The studied factors, that could be influenced on, didn’t seem to be significant in the development of the disease. Instead of addressing these factors, the main focus of knee osteoarhtritis prevention should be to avoid its load-based risk factors, such as overweight.