Hypovitaminosis D is a predictor of aromatase inhibitor musculoskeletal symptoms.

The aromatase inhibitor (AI)-associated musculoskeletal (MSK) pain symptoms are often debilitating and limit compliance with this important hormonal breast cancer therapy. The etiology of this syndrome is unknown. Hypovitaminosis D has been suggested as a possible risk factor for the development of MSK symptoms in women starting AIs. The objective of this substudy was to define the prevalence of low 25(OH)D in this population, to assess risk of low levels on developing pain and to define a target therapeutic goal for 25(OH)D in this population. This analysis was part of a 6-month prospective cohort study examining the MSK side effects of adjuvant AI therapy in postmenopausal women. Patients were evaluated by a rheumatologist with a joint examination, had 25(OH)D levels measured and completed quality of life questionnaires at baseline, 3 and 6 months. Symptomatic patients were defined as those that self-reported new or worsening MSK symptoms. Of 52 patients, 28 (54%) were symptomatic, and two (3.8%) stopped AIs due to MSK ailments. Thirteen patients had objective evidence of tendonitis on rheumatologic examination. Thirty-three percent of all subjects had baseline 25(OH)D levels <40 ng/mL, 19.2% had levels <30 ng/mL and 5.8% had levels <20 ng/mL. Symptomatic patients were more likely to have had baseline levels below 40 ng/mL, compared with asymptomatic patients (46.4% versus 16.7%, p = 0.037). In multivariate regression analyses, levels <40 ng/mL were associated with developing objective tenosynovitis (p = 0.033) but not with developing nonspecific myalgias. Our findings suggest hypovitaminosis D may be contributing to the AI-associated MSK pain syndrome and in particular to the development of tendonitis. Repletion to 25(OH)D levels >40 ng/mL is advisable. Further research should be carried out on identifying additional modifiable risk factors for this syndrome.