Writing in Nutrients, the researchers from China and Australia analysed the results of a three-year multicenter randomised controlled trial known as Vitamin D Effect on Osteoarthritis (VIDEO).
Participants of the trial were suffering from knee OA symptoms such as knee pain, joint stiffness, and physical dysfunction. They were also deficient in serum vitamin D.
Aside from vitamin D, the dietary intake of macroelements among the participants were also recorded using a food frequency questionnaire.
The macroelements were magnesium, potassium, calcium, and phosphorus.
In this post-trial analysis, the researchers studied the relationship between the intake of these four macroelements and changes in knee OA symptoms among the participants.
They studied the dietary intake data of 392 participants who were 50 to 79 years old, suffered from symptomatic knee OA for at least six months, but were not suffering from severe knee pain.
The participants’ quality of life and knee OA symptoms were assessed at baseline and at the 3rd, 6th, 12th, and 24th month using the Western Ontario and McMaster Universities (WOMAC) index.
Magnesium, potassium useful
Findings showed that a higher dietary intake of magnesium and potassium were significantly linked to a reduction in knee OA symptoms.
Among the participants, the average dietary calcium intake was 0.91 g/day, 0.30 g/day for magnesium, 2.86 g/day for potassium, and 1.53 g/day for phosphorus.
Both dietary magnesium and potassium were significantly and negatively associated with total WOMAC index.
For instance, joint stiffness based on the WOMAC index was -76.68 for magnesium and −9.62 for potassium, while that of physical dysfunction was −592.18 for magnesium and −64.64 for potassium.
In contrast, the amount of joint stiffness based on the WOMAC index was -3.91 for calcium and -7.81 for phosphorus.
“Our study, for the first time, illustrated associations of dietary potassium with OA-related outcomes, which suggested a potential protective effect of dietary potassium on OA. More experimental studies are needed to elucidate the underlying mechanisms,” said the researchers.
However, the dietary intake of these magnesium and potassium was not significantly associated with a reduction in knee pain.
In addition, dietary magnesium and potassium were positively associated with lower limb muscle strength at a score of 66.79kg for magnesium and 8.35kg for potassium.
“Studies reported that both dietary intake and serum concentration of magnesium have inverse relationships with radiographic knee OA.
“Low magnesium intake was associated with worse knee cartilage architecture in subjects at risk of knee OA and increased knee pain in subjects with radiographic knee OA.”
Calcium and phosphorus
There was no significant association of dietary calcium and phosphorus with reduction in knee OA symptoms based on the WOMAC index.
“In our study, calcium intake was not associated with the OA-related outcomes. In fact, calcium and magnesium antagonize each other in various physiological activities.
“Competition for serum concentration may also exist between the two macroelements as they compete for intestinal absorption and a high calcium intake leads to increased urine excretion of magnesium,” said the researchers.
However, the study found that dietary phosphorus was significantly associated with greater lower limb muscle strength in knee OA.
This could be because phosphorus is required for maintaining muscle function as it is a substrate for ATP and creatine phosphate synthesis, the researchers explained.
None of the four dietary macroelements were significantly associated with any of the knee joint structures including total cartilage volume, total cartilage defect, total BML, and total effusion-synovitis volume.
Statistically significant Vs clinically meaningful
Although there was a statistically significant association between dietary magnesium and potassium intake and a reduction in knee OA symptoms, it is also important to assess if the results were clinically meaningful, said the researchers.
“Though the associations of magnesium and potassium with WOMAC score were statistically significant, changes would only be clinically meaningful if the WOMAC score decrease by 77.04 given the baseline WOMAC of 642.00 as the minimum clinically important difference of WOMAC score in patients with knee OA is reportedly 12% of the baseline score,” they said.
As such, they said that the changes of WOMAC scores would only be clinical meaningful if dietary magnesium intake was increased by 0.10 g/day and potassium up by 0.88 g/day.
Nonetheless, they also cautioned that it would be difficult to determine the required dosage and which particular subject demographic may benefit most from supplementation of the two nutrients, since the current evidence had come from observational studies.
According to the researchers, this is believed to be the first epidemiological study to examine the longitudinal associations of dietary macroelements with knee joint structures, symptoms, quality of life, and comorbid conditions in symptomatic knee OA patients.
Associations of Dietary Macroelements with Knee Joint Structures, Symptoms, Quality of Life, and Comorbid Conditions in People with Symptomatic Knee Osteoarthritis
Authors: Yan Zhang et al