A new study reveals that black Americans display lower levels of vitamin
D and greater pain sensitivity compared to white Americans. Findings
published in Arthritis
& Rheumatism, a journal of the American College of
Rheumatology (ACR), indicate that vitamin D deficiency may be one of
many factors that account for increased pain in older black Americans
with knee osteoarthritis (OA).
Those with OA experience painful swelling and stiffness of the joints
such as knees, hips and fingers. The National Arthritis Data Workgroup
estimates that 27 million Americans over 25 years of age have OA (based
on 2005 U.S. census data). A long-term study by researchers from the
University of North Carolina—the Johnston County OA Project—suggests
that lifetime risk of developing knee OA is roughly 46%.
During the last decade medical evidence has uncovered the importance of
vitamin D, not only as a vitamin that aids in calcium absorption, but as
a powerful hormone with numerous functions throughout the body. In fact,
studies have found that a decreased vitamin D level reduces immunity and
may contribute to diseases such as cancer and diabetes.
Most vitamin D in humans comes from exposure to the sun, with research
suggesting that a deficiency of this important vitamin may be due to
more indoor activities, increased sunscreen use, and need for longer sun
exposure for those with dark skin pigmentation. One study estimates that
95% of black Americans compared to 70% of white Americans have low
levels of vitamin D.
“People associate vitamin D with good bone health,” said lead author
Toni Glover, MSN, ARNP, a research nurse practitioner and doctoral
candidate at the University of Florida, specializing in the study of
pain in older adults. “Yet, not everyone is aware of what factors
decrease vitamin D and how low levels could contribute to health issues,
including chronic pain.”
Clinical practice guidelines state that vitamin D levels less than 20
ng/mL represent deficiency and levels between 21 and 29 ng/mL represent
insufficiency. Given that low levels of vitamin are linked to chronic
pain and other health conditions, especially in black Americans, the
research team set out to investigate if variations in vitamin D levels
contribute to racial differences in patients with knee pain caused by OA.
With funding from the National Institute on Aging and the John A.
Hartford Foundation and the Mayday Fund, researchers at the University
of Florida and the University of Alabama at Birmingham recruited 94
participants—45 black and 49 white patients with symptomatic knee OA—to
complete questionnaires regarding their symptoms. The study group was
75% female and had an average age of 56 years.
In addition, study subjects underwent testing that included sensitivity
to heat and mechanical pain on the affected knee and the forearm.
Researchers measured heat pain threshold as the point when patients
indicate the sensation “first becomes painful” and pain tolerance when
patients “no longer feel able to tolerate the pain.” Mechanical pain
measures were determined by the patients’ response to pressure in the
knee and forearm.
Despite living in a southern sunny climate, findings indicate that 84%
of black participants had vitamin D levels less than 30 ng/mL compared
to 51% of white subjects. Furthermore, the average vitamin D level for
black Americans was 19.9 ng/mL (deficiency), compared to white Americans
who averaged 28.2 ng/mL (insufficiency). Black participants reported
greater overall knee osteoarthritis pain and those with lower vitamin D
levels displayed greater sensitivity to heat and mechanical pain
(experimental pain).
“Our data demonstrate that differences in experimental pain sensitivity
between the two races are mediated at least in part by variations in
vitamin D levels,” concludes Ms. Glover. “However, further studies are
needed to fully understand the link between low vitamin D levels and
racial disparities in pain. Although rare, vitamin D toxicity is
possible and older adults should consult with their primary care
provider regarding supplementation. It may be warranted that older black
Americans with chronic widespread pain be screened for vitamin D
deficiency to reduce disparities in pain.” The authors plan to pursue
additional research which tests the impact of improving vitamin D status
on chronic pain for older black and white Americans.
