To the Editor: Vitamin D deficiency or insufficiency and urinary incontinence (UI) are both common in older women. Lower vitamin D level is associated with muscle weakness1,2 and falls.3 Higher vitamin D intake was associated with a lower risk for overactive bladder in women aged 40 and older.4 Another study further revealed that the risk of UI was 45% lower in people with vitamin D levels of 30 ng/mL or higher than in those with inadequate levels.5 This letter reports on two adult women with UI who responded to “adequate” vitamin D supplementation (with posttreatment levels >40 ng/mL). A 78-year-old woman with a long history of allergic rhinitis, well-controlled asthma, and hyperlipidemia had UI for longer than 6 months. The symptoms were consistent with urge type, and she had to wear pads for protection. She was fully functioning and still worked part time. She had had a hysterectomy 36 years before and had one full-term pregnancy (with vaginal delivery). Medications included omeprazole, inhaled corticosteroid, fexofenadine, corticosteroid nasal spray, inhaled albuterol, a statin, and multiple vitamins. She had been taking 50,000 IU of vitamin D2 twice a month after her 25-hydroxy (OH) vitamin D (25(OH)D) level was found to be 10 ng/mL (normal 30–100 ng/mL) 1 year before. She had also been diagnosed with vitamin B12 deficiency 1.5 years before, and had received cobalamin injections since them. Her weight was 75.8 kg, and her height was 1.68 m (body mass index (BMI)=26.9 kg/m2). Physical examination revealed congested turbinates and a surgical scar on the abdomen and nothing else remarkable. Laboratory tests including complete blood count (CBC), chemistry, thyroid function test, sedimentation rate, and urinalysis were all normal; rechecked 25(OH)D level was 21 ng/mL, despite being treated with 100,000 IU monthly for 1 year. She refused gynecological referral as she felt her condition was not “correctable.” She was treated with vitamin D2 50,000 IU weekly. At her 6-month follow-up visit, she reported that her UI had resolved and that she had not had worn a protection pad for a month. Her rechecked 25(OH) vitamin D level was 54 ng/mL. No other events or interventions occurred during the 6-month period. A 59-year-old woman with a long history of allergic rhinitis on her first visit complained of chronic multiple joint pains and UI, which mainly occurred when she stood up or sneezed, for several months. She denied symptoms suggestive of cystitis. She had no history of hysterectomy or bladder surgery. Medications included corticosteroid nasal spray, acetaminophen, desloratadine, and sertraline. She occasionally took ibuprofen for pain. On review of systems, she denied symptoms suggestive of polymalgia rheumatica or rheumatoid arthritis. Her weight was 67 kg, and her height was 1.60 m (BMI 26.2 kg/m2). Physical examination revealed nasal drainage and congested turbinates; results of other examinations, including the musculoskeletal system, were unremarkable. Laboratory tests, including CBC, chemistry, thyroid function test, and urinalysis were all normal, except 25(OH)D level (13 ng/mL) and sedimentation rate (113 mm; normal 0–30 mm). She was referred to a gynecologist who gave a diagnosis of “loss of external sphincter control.” Pelvic floor muscle exercise was recommended, and she refused further exercise after she experienced muscle pain and ache in the pelvic and hip areas in 2 weeks. After aggressive vitamin D2 supplementation (50,000IU weekly for 12 weeks), her 25(OH)D level rose to 43 ng/mL, and her sedimentation rate was 10 at a 6-week follow-up blood test. She reported that her UI had resolved, and her joint pain had significantly improved at a 3-month follow-up visit. She continued to take vitamin D2 50,000 IU three times a month, and her most recent blood level was 70 ng/mL. No events occurred between these two visits. These two cases suggest that vitamin D deficiency is the underlying condition associated with UI. Significant improvement in UI after “adequate” vitamin D blood levels have been achieved with aggressive treatment supports this. Side effects resulting from the use of medications such as corticosteroids or antihistamines that may have contributed to UI are unlikely because there were no changes in these medication uses in either of these cases. There is debate as to what blood levels are considered “adequate” for vitamin D supplementation and on what indication treated for—because cancer prevention may require a higher blood level.6 Future studies such as a clinical trial will further illustrate the relationship between vitamin D deficiency and UI. Conflicts of Interest: The author reported no financial conflicts with this research topic and contents. Author Contributions: Dr. Gau takes a full responsibility for the integrity and the accuracy of this case report. Sponsor's Role: None.