According to findings published in The Clinical Journal of Pain, adequate vitamin D levels were associated with significantly lower knee pain scores, compared to participants with deficient or insufficient levels.
In addition, performance in tasks such as standing from a seated position was also significantly better in people with adequate levels, compared to obese people with deficient or insufficient vitamin D levels.
“Adequate vitamin D may be significant to improving osteoarthritis pain because it affects bone quality and protects cell function to help reduce inflammation. Vitamin D maintains calcium and phosphate concentration levels to keep bones strong,” said lead author Toni Glover.
The new study shows correlation and not causation, and the potential mechanism to explain the association between vitamin D levels and improved function is not fully known, said the researchers.
Dr Glover added: “Increased pain due to osteoarthritis could limit physical activity, including outdoor activity, which would lead to both decreased vitamin D levels and increased obesity.”
The sunshine vitamin
According to the 2014 CRN Consumer Survey on Dietary Supplements, vitamin D is the second leading category among supplement users after multivitamins.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 and -2 diabetes.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Dr Glover and her colleagues analyzed data from 256 people with an average age of 56.8. Vitamin D levels were obtained from blood samples, while knee pain was assessed using lower extremity functional performance tests.
Results showed that obese people with adequate vitamin D levels were associated with better walking, balancing and rising from sitting to standing, compared to obese people with insufficient D levels. Lower pain scores were also observed for people with higher vitamin D levels.
“Vitamin D is inexpensive, available over-the-counter and toxicity is fairly rare,” said Dr Glover. “Older obese patients with chronic pain should discuss their vitamin D status with their primary care provider. If it’s low, take a supplement and get judicious sun exposure.”
Source: The Clinical Journal of Pain
Published online ahead of print, doi: 10.1097/AJP.0000000000000210
“A Cross-Sectional Examination of Vitamin D, Obesity, and Measures of Pain and Function in Middle-Aged and Older Adults with Knee Osteoarthritis”
Authors: T.L. Glover, B.R. Goodin, C.D. King, et al.