A study published in AgResearch magazine shows that low vitamin D in your diet may increase the risk of developing the painful condition known as osteoarthritis in the knees.
Osteoarthritis occurs when the natural cushioning between joints in the body wears away—allowing bones to rub together.The researchers investigated the possible interaction between circulating blood levels of both vitamin D and parathyroid hormone (PTH) on the progression of knee osteoarthritis in adults. PTH is involved in vitamin D metabolism. The scientists looked at a subset of data collected during a longitudinal study called the Osteoarthritis Initiative, or OAI, which is a large study of individuals with, or at risk of, knee osteoarthritis.
The OAI study participants, aged 45–79, had at least one knee with evidence of osteoarthritis. The researchers focused on a total of 418 volunteers for whom blood serum concentrations of vitamin D and PTH were available and for whom radiographs to assess knee osteoarthritis progression were available. The volunteers' were followed for four years, during which time knee osteoarthritis progression was tracked and related to vitamin D and PTH levels in the blood.
The researchers found that compared to volunteers with healthy levels, participants with low vitamin D levels had more than double the risk of their knee osteoarthritis worsening during the study. People who had both low vitamin D and high PTH concentrations were more than three times more likely to get worse during the study than those with normal levels of both.
Inadequate vitamin D was defined as those with less than 15 nanograms per milliliter of blood serum, consistent with the Institute of Medicine (IOM) recommended vitamin D dietary allowance, which is at least 600 International Units (IU) daily for those aged 4–70 and 800 IU for adults over 70.
The researchers concluded that vitamin D deficiency is a risk factor for increased knee osteoarthritis progression, and that increased, adequate dietary intake may be beneficial in those with knee osteoarthritis.