Dr. Michelle A. Petri, Ph.D., director of the Hopkins Lupus Center is the lead author of the study, and the findings were presented at the American College of Rheumatology/Association of Rheumatology Health Professionals (ACR/ARHP) Annual Meeting in San Diego, CA.
The disease can affect various organ systems, from the cardiovascular and immune systems to vital organs such as the lungs and the kidneys.
As Dr. Petri and her colleagues write in their paper, levels of vitamin D are known to be low in patients with lupus. So, the team set out to examine the role of vitamin D in patients with systemic lupus erythematosus (SLE), which is the most common form of the disease.
Studying vitamin D levels in lupus patients
Dr. Petri and her team examined the clinical data available on 1,392 lupus patients, 92 percent of whom were female. On average, the patients were 47.3 years old.
The researchers had access to the patients' vitamin D levels when they first visited the doctor, as well as to the state of their organs and tissues during the follow-up visits.
Levels of the vitamin were assessed using 25-hydroxy vitamin D – a common and accurate way of ascertaining vitamin D levels.
Based on the first measurements of vitamin D, patients were grouped into those with less than 20 nanograms per milliliter (ng/ml) of 25-hydroxy vitamin D, and those with more than 20 ng/ml.
Overall, 27.3 percent of the patients had deficient levels of vitamin D at their first medical visit.
Using the Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR) Damage Index, the researchers evaluated the "risk of lifetime organ damage."
The organ systems considered included the neuropsychiatric, pulmonary, cardiovascular, gastrointestinal, and musculoskeletal system.
Then, the researchers adjusted this risk for age, gender, and ethnic background.
Low vitamin D may predict renal failure
The study found that lupus patients with deficient levels of vitamin D had the highest relative risk of renal damage.
These patients were also at a higher risk of skin damage and total organ damage.
The researchers found no association with damage to any of the other organs considered.
"Low vitamin D associated with total damage and with end-stage renal disease," conclude the authors. "Surprisingly," the authors add, "low vitamin D did not associate with musculoskeletal damage," including osteoporotic fractures.
"We have shown that supplementing vitamin D reduces urine protein, which is the best predictor of future renal failure," says Dr. Petri.
The lead author of the study also suggests that vitamin D supplementation may be a valid pathway for the prevention of renal damage in lupus.
"Supplementary vitamin D is very safe [...] It helps to prevent one of the most dreaded complications of [lupus], and likely has a role in preventing blood clots and cardiovascular disease as well. Vitamin D supplementation, which can reduce proteinuria, should be a part of the treatment plan for lupus [...] patients."
Dr. Michelle A. Petri
Proteinuria is the medical term for excessive quantities of protein in one's urine.
According to the Centers for Disease Control and Prevention (CDC), lupus affects anywhere between 161,000 and 322,000 Americans, with women being far more affected than men.
For women, the risk of developing lupus is anywhere between "four to 12 women for every one man."