Vitamin D and its importance

Vitamin D, also known as calciferol, is a fat-soluble vitamin with its primary function related to musculoskeletal health. It stands as the most common nutritional deficiency globally, mainly due to inadequate sun exposure. While various general health benefits have been identified, there is no general consensus on supplementation or treatment.

The primary source of vitamin D is sunlight exposure (UV-B). The liver and kidneys also play roles in converting it into its active form. Only 10% of vitamin D comes from the diet.

Function

Main Musculoskeletal Function:

• Increases calcium and phosphate gut absorption
• Facilitates bone mineralization (interaction with PTH)

Other Novel Functions:

• Immune modulation
• Cancer prevention

When to do a blood serum screen for vitamin D level?

Most guidelines do not recommend screening vitamin D levels in the general population, as results would often show mild insufficiency that may or may not be due to fluctuations in sun exposure, and most individuals may not benefit from vitamin supplements (sensible sun exposure is recommended for most).

Screening is rational for those at risk of vitamin D deficiency who are likely to benefit from supplementation. Indications for screening, according to Australian guidelines, include:

• Institutionalized/housebound individuals (e.g., chronic disease, disability)
• Dark-skinned individuals
• Those with medical conditions such as liver disease (e.g., cirrhosis), kidney disease (e.g., ESRD), hyperparathyroidism
• Individuals on certain drugs like rifampicin, anti-epileptics, glucocorticoids, some anti-HIV drugs
• Conditions causing fat malabsorption, such as cystic fibrosis, celiac disease, inflammatory bowel disease (Crohn’s disease), gastrectomy, short bowel syndrome

Vitamin D level criteria

Vitamin D serum levels are measured as 25-hydroxyvitamin D (vitamin D2, ergocalciferol). Levels fluctuate mainly due to sun exposure during seasonal changes (excluding people in tropical regions), with summer usually having the highest levels.

Vitamin D2	(nanomol/L)	(nanogram/mL)
Deficiency	< 50	< 20
Insufficiency	52-72	21 – 29
Normal	75- 200	30 – 100
Toxicity	> 375	> 150

Sign and symptoms

Most people with insufficiency/deficiency are asymptomatic. Severe prolonged deficiency can lead to various bone-related symptoms.

Children (Skeletally immature)

• Growth retardation
• Rickets

Adults

• Osteomalacia
• Osteopenia
• Osteoporosis

Sensible sun exposure (UV-B)

Recommended for both treatment and prevention. It has more benefits than risks (skin cancer). Exposure of arms and legs for 5-30 minutes between 10 am to 3 pm in summer with face protection is suggested. Always avoid sunburn.

Treatment indications

While sensible sun exposure is best for all patients, dietary supplements/treatment is recommended in the following groups:

• Uncomplicated moderate – severe vitamin D deficiency (25-hydroxyvitamin D < 30 nanomol/L)
• Osteoporosis with vitamin D deficiency
• Osteomalacia, rickets

Treatment regimen

Uncomplicated mild deficiency

• Vitamin D2 1,500-2,000 IU PO OD or
• Vitamin D3 1,000-2,000 IU PO OD or Vitamin D3 7,000-14,000 IU PO weekly

Uncomplicated moderate – severe deficiency

Consolidate phase (for 6-8 weeks)

• Vitamin D2 6,000 IU PO OD or Vitamin D2 50,000 IU PO weekly or
• Vitamin D3 3,000-5,000 IU PO OD

Maintainance phase

• Vitamin D2 1,500-2,000 IU PO OD or
• Vitamin D3 1,000-2,000 IU PO OD or Vitamin D3 7,000-14,000 IU PO weekly

Calcium supplement

1-2 g/day divide in 3-4 doses (in elemental calcium)