What vitamins are produced endogenously (within the body)?

From the Guidelines

The human body is capable of endogenously producing vitamins D, K2, biotin, and niacin, as well as converting beta-carotene into vitamin A, highlighting the importance of sun exposure, gut health, and dietary intake for optimal vitamin levels. When considering the endogenous production of vitamins, it's essential to understand the processes involved. Vitamin D, for instance, is synthesized in the skin upon exposure to sunlight, specifically UVB radiation, which converts 7-dehydrocholesterol to previtamin D3, as noted in a study on the implications of vitamin D for cardiovascular disease 1.

Key Endogenously Produced Vitamins

• Vitamin D: synthesized in the skin from 7-dehydrocholesterol upon UVB radiation exposure, with sun exposure being a significant source of vitamin D production, as seen in light-skinned individuals who can produce tens of thousands of units of cholecalciferol from just 15 minutes of sun exposure per week 1.
• Vitamin K2 (menaquinone): produced by gut bacteria, emphasizing the role of intestinal health in vitamin production.
• Biotin (vitamin B7): also synthesized by intestinal bacteria, though the amounts may not be sufficient to meet full bodily requirements.
• Niacin (vitamin B3): can be produced from the amino acid tryptophan, albeit through an inefficient conversion process.
• Vitamin A: can be produced in small amounts from beta-carotene and other carotenoids found in the diet, contributing to the body's vitamin A levels.

Importance of Dietary Intake and Health Factors

Given that the body's endogenous production of these vitamins can be influenced by various factors such as sun exposure, gut health, and dietary consumption of precursor nutrients, it's crucial to maintain a balanced diet and healthy lifestyle to support optimal vitamin levels and overall well-being.

From the Research

Endogenously Produced Vitamins

• Vitamin D is produced endogenously in the skin upon exposure to sunlight 2, 3, 4, 5

Details of Endogenous Production

• The skin contains the provitamin D3 7-dehydrocholesterol, a precursor of vitamin D, which is photoconverted to previtamin D3 by UVB radiation 4
• Vitamin D is then converted by the liver to 25-hydroxyvitamin D, its major circulating form, and later by the kidney to 1,25-dihydroxyvitamin D, the biologically active form 3

Other Vitamins

• There is evidence that vitamin B-12 is synthesized and utilized by bacteria in the human gut microbiome 6
• However, it is not clear if vitamin B-12 is produced endogenously in humans in significant amounts 6