Can Vitamin D help prevent the onset of osteoarthritis (OA) or slow joint damage if you already have OA? While study results have been mixed, in general, they suggest that Vitamin D may be protective in OA.
Vitamin D promotes calcium absorption by the body to enable bone growth and repair. Because osteoarthritis has a bone growth component, researchers have been examining the potential role of vitamin D in osteoarthritis development and progression.
What the Studies Show
Two studies published in 2014 looked at vitamin D levels in the blood of people with or at risk of OA. A study published in The Journal of Nutrition found that participants with low vitamin D levels had a more than 2-fold elevated risk of knee OA progression compared with those with greater vitamin D concentrations. The other, published in Annals of Rheumatic Diseases, found that among older adults, moderate vitamin D deficiency predicted new or worsening knee pain over 5 years.
A third 2014 study published in Arthritis Care and Research asked more than 2,000 people with knee osteoarthritis about their milk consumption during the prior year. They found that those with the self-reported highest milk intake (7 or more glasses per week) had the least amount of joint-space narrowing (a measure of OA progression). This study did not, however, measure blood levels of vitamin D, so there is no way to know if it was vitamin D, another component of milk or an unrelated factor that influenced OA progression.
High-quality controlled trials, however, show less definitive results.
One randomized, controlled trial of vitamin D and OA was published in 2013 in Clinical Orthopaedics and Related Research. Scientists in India separated 107 people with knee OA and vitamin D deficiency into two groups: one group received supplements and the other did not. After 1 year, the researchers found a small decrease in knee pain and an improvement in knee function among the vitamin D-treated group, but not the placebo group.
Another randomized, controlled trial – published in JAMA in 2013 — did not find a protective relationship. Researchers studied 146 people with knee OA, half of whom received vitamin D supplements, for 2 years. When compared with the placebo group, the supplemented group did not have improved knee pain or less cartilage loss.
Lead study author Timothy McAlindon, chief of the division of rheumatology at Tufts Medical Center in Boston, believes the different results may have been that the India study looked at people with knee OA who were medically deficient in Vitamin D. The participants in McAlindon’s study had normal vitamin D levels to begin with and were getting an extra boost. The scientists in India weren’t just enhancing the participants’ levels, they were replacing a true deficiency.
Getting Enough Vitamin D
Vitamin D is naturally synthesized by the body when ultraviolet B (UVB) rays from the sun reach your skin directly (not through a window). The amount of sun time needed for adequate vitamin D synthesis depends on several factors: skin tone, time of year, distance from the equator and amount of skin exposed. Light-skinned people wearing a tank top and shorts in the Southern United States may need only 10 minutes of sun exposure per day. Dark-skinned people living in Canada may not be able to get enough UVB exposure to produce adequate vitamin D. Despite the importance of the sun to vitamin D synthesis, it is wise to limit exposure of skin to ultraviolet rays to lower your risk for skin cancer.
Vitamin D can be consumed in foods like fatty fish (salmon, tuna, mackerel) or in fortified products like milk, yogurt and some orange juices. If you’re not getting enough through your food, supplements can be taken.
Overdosing on this fat-soluble vitamin, however, can be dangerous. Aim for the recommended 600 International Units of vitamin D per day, not more.
The Bottom Line
Dr. McAlindon’s bottom line take on Vitamin D: “Overall, the potential role of vitamin D in preventing the development of or slowing the progression of osteoarthritis is under active investigation. Results are conflicting, hard to interpret and prone to bias. At this point there is no compelling reason to supplement your diet with Vitamin D solely for possible slowing of your OA or reduction of OA symptoms. Getting adequate Vitamin D through sun exposure and your diet are important for general well-being, bone health, osteoporosis prevention and muscle function. In parts of the world where people are medically deficient in Vitamin D, supplementing the diet could potentially help their joint symptoms along with their overall health.”
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