I recently encountered a middle-aged female patient who presented with a two-year history of fatigue and mood changes. She reported seeing multiple providers for the condition, but had come to terms with the idea that it was simply the result of aging.

The patient’s very subjective symptoms suggested a number of diverse differential diagnoses. She had recently moved to North Carolina from Chicago, and I was fortunate to have a stack of her past medical records, which contained the information necessary for me to cross many conditions off my list.

Having recently read about the increasing prevalence of vitamin D deficiency, I decided to evaluate this patient’s vitamin D levels. Sure enough, they came back as 19 ng/ml. The Institute of Medicine defines vitamin D insufficiency as 12 to 20 ng/ml, and deficiency as less than 12 ng/ml. Serum levels higher than 20 ng/ml are adequate for bone health, although adequate levels for prevention of other illnesses may be higher.

Risk factors for Vitamin D insufficiency include:

  • Old age
  • Darker skin pigmentation
  • Obesity
  • Pregnancy
  • History of osteoporosis or malabsorption disorders
  • Taking phenytoin, a drug that accelerates vitamin D metabolism
  • Residing at latitude of 37° or higher

Vitamin D is an essential vitamin with a long-known history of regulatory effects on calcium, and the ability to prevent rickets and osteoporosis. The nutrient permits calcium to enter the body’s cells and enhances phosphorous absorption, supporting bone mineralization and health. Vitamin D receptors are present in multiple body tissues, which allows it to function similarly to hormones and play a role in multiple organ systems.

The most recent CDC-recommended dietary allowances for vitamin D are as follows:  

  • 400 IU for infants to 12 months of age
  • 600 IU for those aged 1 year to 70 years
  • 800 IU for those aged 70 years and older

These recommendations are based on the average daily level of intake sufficient to meet the nutrient requirements of 98% of healthy people.

Vitamin D sources include exposure of skin to direct sunlight, dietary fortified sources (including milk, orange juice, fish, and some breads and cereals) and oral supplementation. Although the main source of vitamin D is ultraviolet B rays from the sun, the increased risk for skin cancer with sun exposure presents a challenge to achieving healthy levels while avoiding detrimental effects.

For this patient, I prescribed 50,000 u/day oral vitamin D3 once daily for eight weeks to begin repletion. Following this course, a repeat level will need to be assessed, and the patient will likely need to continue daily supplementation with 800 u/day. I anticipate that this patient will report an improvement in symptoms after adequate vitamin D levels are achieved.

It is important in primary care not to overlook the practice of appropriately screening patients for vitamin D deficiency. This case highlights how taking an appropriate history can go a long way towards identifying at-risk patients.

Leigh Montejo, MSN, FNP-BC, provides health care to underserved populations at the Metropolitan Community Health Service’s Agape Clinic in Washington, North Carolina.