Vitamin D

Takeaways

  • 15-20 minutes of sun.
  • Oily fish, egg yolks.

Summary

  • Obtained from diet or synthesized in the skin.
    • After exposure to UV B light.
    • Vitamin D levels fluctuate seasonally.
    • Reliance on dietary sources of vitamin D is greatest during the winter.
  • UV B radiation.
    • Wavelengths of 290–315 nm.
    • Affected by latitude, altitude, air quality, cloud cover, time of day, time of year.
    • Affected by sunscreen, clothing.
    • Affected by skin pigmentation, age.
  • Diet.
    • Oily fish, egg yolks.
    • Animal products (muscle, liver, fat, and kidney).
  • Various forms of vitamin D circulate in the body.
    • Within certain boundaries.
    • Regulate vitamin D activity and signaling.
  • Classical actions of vitamin D:
    • Promote calcium homeostasis.
    • Promote bone health.
  • Additional benefits.
    • Functioning of immune, cardiovascular, and reproductive systems.
    • Many tissues have vitamin D responsive elements.
  • For instance, immunologic effects.
    • Ability to maintain tolerance and to promote protective immunity.
    • Lower levels of vitamin D associated with higher levels of infection.
    • Through a number of pathways, vitamin D:
      • Reduces production of inflammatory cytokines.
      • Increases production of anti-inflammatory cytokines.
      • Avoids over-stimulation (autoimmune diseases).
      • Avoids under-stimulation (spread of infection).
  • Vitamin D deficiency linked to various illnesses:
    • Diabetes, multiple sclerosis, and several cancers.
    • Susceptibility to infection and autoimmune diseases.
  • Vitamin D supply to tissues important at specific times of life.
    • Older persons (reducing susceptibility to chronic degenerative diseases).
    • Fetus (organogenesis).
    • Childhood and adolescence (bone mineral accrual and somatic growth).
  • Intervention trials have rarely shown benefits of vitamin D supplementation as treatments or preventive measures.

 

Leave a Reply