What is Vitamin D?

Vitamin D is a fat-soluble vitamin that functions like a hormone in the body. It's essential for: < /p>

• Calcium Absorption: Helps the body absorb calcium from the gut
• Bone Health: Critical for strong bones; deficiency leads to weak, soft bones
• Muscle Function, Immune System, Mood

How Do We Get Vitamin D?

• Sunlight (Primary Source): Skin produces Vitamin D when exposed to UVB rays
• Diet: Fatty fish (salmon, mackerel), fortified milk/cereals, egg yolks
• Supplements: Vitamin D2 (ergocalciferol) or D3 (cholecalciferol—preferred)

How Common is Deficiency?

• Very common: Affects ~40-50% of the global population
• Higher rates in older adults, people with dark skin, those who avoid sun exposure, obese individuals

Causes of Vitamin D Deficiency:

• Inadequate Sun Exposure: Indoor lifestyle, living in northern latitudes, winter months, sunscreen use
• Dark Skin: Melanin reduces Vitamin D production
• Obesity: Vitamin D is fat-soluble and gets "trapped" in fat tissue
• Malabsorption: Celiac disease, Crohn's disease, cystic fibrosis, gastric bypass surgery
• Chronic Kidney Disease: Kidneys convert Vitamin D to its active form (calcitriol); kidney disease impairs this
• Liver Disease: Liver activates Vitamin D; cirrhosis reduces activation
• Medications: Anticonvulsants, glucocorticoids, antifungals, HIV medications
• Aging: Skin becomes less efficient at making Vitamin D
• Limited Dietary Intake: Vegan diet, lactose intolerance

Symptoms:

Mild Deficiency:

• Often asymptomatic
• Fatigue, general aches and pains
• Frequent infections
• Mood changes (depression)

Severe/Prolonged Deficiency:

• Adults:
  • Osteomalacia: Soft bones causing bone pain, muscle weakness, difficulty walking
  • Osteoporosis: Increased fracture risk
• Children:
  • Rickets: Bowed legs, delayed growth, bone deformities, muscle weakness
• Secondary Hyperparathyroidism: Low Vitamin D → low calcium → parathyroid glands overproduce PTH to compensate → pulls calcium from bones

Diagnosis:

Labs:

• 25-OH Vitamin D (Calcidiol): Best measure of Vitamin D status
  • Deficiency: <20 ng/mL (50 nmol/L)
  • Insufficiency: 20-30 ng/mL (50-75 nmol/L)
  • Sufficient: ≥30 ng/mL (75 nmol/L)
  • Optimal (for bone health): 30-50 ng/mL
• Calcium: May be low or normal (body compensates)
• Phosphorus: May be low
• PTH: Elevated (secondary hyperparathyroidism)
• Alkaline Phosphatase: Elevated (in osteomalacia/rickets)

Treatment:

Goal: Raise 25-OH Vitamin D to ≥30 ng/mL

Vitamin D Supplementation:

• Vitamin D3 (Cholecalciferol): Preferred (more effective than D2)
• For Deficiency (<20 ng/mL):
  • Loading Dose: 50,000 IU weekly for 6-8 weeks
  • Maintenance: 1000-2000 IU daily (or 50,000 IU monthly)
• For Insufficiency (20-30 ng/mL):
  • 1000-2000 IU daily
• For Prevention/Maintenance (if sufficient):
  • 600-800 IU daily (general population)
  • 1000-2000 IU daily (older adults, at-risk groups)

Higher Doses May Be Needed For:

• Obesity (2-3x normal dose)
• Malabsorption disorders
• Medications interfering with Vitamin D metabolism

Calcium Supplementation:

• Often needed if calcium intake is inadequate
• 1000-1200 mg/day (total from diet + supplements)

Sunlight Exposure:

• 10-30 minutes of midday sun exposure (without sunscreen) several times per week can help
• Not always practical or safe (skin cancer risk); supplementation more reliable

Monitoring:

• Recheck 25-OH Vitamin D: 3-6 months after starting treatment
• Once Sufficient: Recheck annually or as clinically indicated
• Avoid Over-Supplementation: Levels >50-60 ng/mL not beneficial and may increase risk of toxicity

Vitamin D Toxicity (Very Rare with Supplements):

• Requires very high doses (>10,000 IU/day for months)
• Symptoms: Hypercalcemia (nausea, vomiting, weakness, kidney stones, confusion)
• Levels >100 ng/mL indicate toxicity

Benefits of Treatment:

• Improved bone density, reduced fracture risk
• Improved muscle strength, reduced fall risk
• Better immune function
• Possible improvement in mood

Who Should Be Screened?

• Patients with osteoporosis or osteopenia
• Older adults (especially those at risk for falls/fractures)
• Chronic kidney disease, liver disease
• Malabsorption syndromes
• Obesity
• Dark-skinned individuals with limited sun exposure
• Pregnant or breastfeeding women
• On medications affecting Vitamin D metabolism