Vitamin D: a hormone for all seasons

Area of Science:

• Endocrinology
• Nutritional Science
• Bone Biology

Background:

• Vitamin D synthesis begins in the skin via UVB irradiation of 7-dehydrocholesterol.
• Metabolites include 25-hydroxyvitamin D (circulating) and 1,25-dihydroxyvitamin D (hormonal form).
• Primary role is enhancing intestinal calcium and phosphate absorption, preserving bone integrity.

Purpose of the Study:

• To review the functions and optimal blood levels of vitamin D.
• To explore the role of vitamin D in bone health, immune function, and chronic disease prevention.
• To discuss the interplay between vitamin D and calcium.

Main Methods:

• Literature review of vitamin D metabolism, function, and health implications.
• Analysis of evidence supporting target blood levels for 25-hydroxyvitamin D.
• Examination of vitamin D's role in calcium absorption, bone health, and disease risk reduction.

Main Results:

• Optimal blood levels for 25-hydroxyvitamin D are recommended at least 50 nmol/l, potentially higher (75-80 nmol/l).
• Vitamin D and calcium intake reduce falls and fractures in the elderly.
• Emerging evidence links adequate vitamin D to reduced cancer, autoimmune disease, improved immunity, cardiovascular health, and reduced type 2 diabetes.

Conclusions:

• Vitamin D is essential for calcium homeostasis and bone health.
• Adequate vitamin D levels offer broad health benefits beyond bone, including immune and metabolic functions.
• Combined vitamin D and calcium intake is vital for preventing falls and fractures in older adults.