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.