Vitamin D deficiency and insufficiency affects approximately 70% of Americans. One in 4 adults over the age of 60 takes vitamin D supplements in hopes of counteracting the deficit, though in an attempt to treat this, some patients are self-medicating with mega-doses leading to instances of intoxication and a risk of life-threatening hypercalcemia.
Healthcare providers should ask their patients about their use of vitamin D supplementation. A recent article in The Nurse Practitioner summarizes the key information around vitamin D and why it’s vital for health providers to assess risk factors for deficiency—and toxicity—as part of a patient’s regular preventative care.
Vitamin D has well-known benefits to the musculoskeletal system, and an important role in calcium regulation, but the connection with other disease processes is less clear. Low levels of vitamin D are associated with many chronic illnesses, though a causative role has yet to be established.
Eighty to one hundred percent of vitamin D intake is through cutaneous synthesis, though specific UVB levels absorbed depends on patient’s age, skin pigmentation, as well as environmental factors like month, latitude, season, and cloud cover. Patients at risk for a vitamin D deficiency include those with limited sun exposure, highly pigmented skin, high body mass index, and poor nutritional intake. Also at risk are older adults, pregnant women, breast-fed infants, and patients with certain chronic conditions. Those conditions include diabetes, liver and kidney disease, inflammatory bowel disease, cystic fibrosis, malabsorptive illness caused by gastric bypass surgery, psychiatric and neurological disorders, non-specific musculoskeletal pain, or epilepsy (when on antiepileptic drugs).
Vitamin D is measured by serum 25(OH)D levels which represent collective intake by sun exposure, food and supplements and is most commonly reported by laboratories in ng/mL. Levels of 25(OH)D are categorized by the National Institutes of Health Guidelines as deficiency (<12ng/mL), insufficiency (12 to <20 ng/mL), sufficiency (≥ 20ng/mL), and excess (>50ng/mL).
Patients with risk factors should be tested for 25(OH)D and calcium levels as part of their annual preventive health maintenance, though testing of the patients without risk factors is not recommended.
Determining the recommended daily intake (RDI) for individuals can be challenging because the lack of ability to predict how much vitamin D someone receives from sun exposure, but the Institute of Medicine’s RDI for most adults is 600 international units (IU), or 800 IU for adults 70 years or older with a maximum safe RDI of 4,000 IU.
Additional sun exposure is not recommended to treat vitamin D deficiencies due to the risk of skin cancer, making diet and supplements the main source for patients with a deficiency. Meeting the RDI through diet alone can be difficult, but the best sources for vitamin D are animal-based foods like fatty fish (a serving of salmon provides between 600 and 1,000 IU of vitamin D) or fortified foods, such as milk (115 IU per serving). The two types of vitamin D most commonly used for supplementation are vitamin D2 (ergocalciferol), which is derived from plant sources, and vitamin D3 (cholecalciferol), which is created by the irradiation of lamb’s wool. Both are available in pill form over the counter, with D2 also available by prescription.
Prescribed dosages of supplements need to be tailored to the needs of the individual and take into account drug interactions and comorbidities. Drugs that can interfere with absorption of vitamin D including corticosteroids, cholestyramine, orlistat, antiepileptic drugs and anti-tuberculosis drugs. Patients with malabsorption or comorbidities may need higher doses to achieve vitamin D sufficiency.
It is key to treat low vitamin D levels as there are a number of diseases where deficiency has been found to be a risk factor including: all-cause dementia and Alzheimer’s disease, rickets, cardiovascular disease, and respiratory infections. Patients with certain conditions have specific risks associated with vitamin D deficiency including: patients with IBD, who have an increased risk of hospitalization, patients with breast and colon cancer, who have an increased risk of mortality, and older adults who have a higher risk for falling.
Though rare, vitamin D intoxication can happen, often through the over self-administration of supplements. The diagnostic findings include 25(OH)D levels above 150ng/mL and calcium levels between 12 and 16 mg/DL. Left untreated, intoxication can lead to toxicity which can lead to life-threatening hypercalcemia and acute kidney injury. Symptoms and signs of intoxication may include abdominal pain, muscle or bone pain, weight loss, skin excoriations, and lethargy.
Treatment for intoxication should be tailored to reflect the duration and severity of the toxicity, as well as patient’s age and comorbidities, but often involve ceasing all vitamin D and calcium supplements and could include isotonic I.V. fluids (typically 0.9% sodium chloride for a minimum urine output of 100 mL/hour), bisphosphonates, calcitonin, and corticosteroids.