Nightly repair after big nights

Collagen is the most abundant protein in your body, forming the structural framework of connective tissue in tendons, ligaments, cartilage, skin and blood vessel walls. Vitamin C is an essential cofactor for the enzymes that convert proline and lysine into hydroxyproline and hydroxylysine, the modified amino acids that give collagen its strength and structural integrity. Without adequate vitamin C, these enzymatic reactions cannot complete and collagen produced is structurally weak. This is the mechanism behind scurvy, the historical vitamin C deficiency disease, whose symptoms of joint pain, bleeding gums and impaired wound healing all reflect connective tissue breakdown. Modern diets rarely produce clinical scurvy, but sub-optimal vitamin C status, below the plasma level associated with optimal collagen synthesis, is common and contributes to slower tissue repair and joint recovery in people with high physical loads.

What is happening

The collagen synthesis that uses vitamin C occurs primarily during sleep, driven by the overnight peak in growth hormone that coordinates tissue repair across the body. During physically demanding work, microscopic damage to connective tissue, the tendons, ligaments and fascial planes that sustain repeated load throughout a long shift, is repaired through collagen synthesis in the recovery hours. Adequate vitamin C availability during this window supports complete repair. Insufficient vitamin C limits it, contributing to the gradual accumulation of unresolved tissue damage that produces the joint stiffness, tendon soreness and reduced mobility that build across a demanding season rather than resolving overnight.

Vitamin C also plays a central role in immune restoration during sleep. Natural killer cell function, infection-fighting white blood cell activity and immune cell growth and multiplication all depend on vitamin C as a cofactor and antioxidant protector. During active infection or sustained immune activation from repeated threat exposure, plasma vitamin C levels deplete rapidly because immune cells consume it at an accelerated rate during the oxidative burst they use to destroy threats. Replenishing vitamin C through diet or supplementation during and after illness or high-exposure periods supports the immune restoration that sleep facilitates, providing the raw material for the immune cell production that the sleep hormonal environment is driving.

What to do next

The most consistent evidence for vitamin C's practical benefit is in populations under high physical and psychological stress, including athletes, healthcare workers and people working demanding occupational schedules. In these groups, supplementation of 200 to 1000 milligrams per day has been shown to reduce the incidence and duration of upper respiratory infections, support faster tissue recovery and maintain antioxidant capacity under conditions that deplete it. Food sources sufficient for these effects include one medium red pepper (170mg), one kiwi fruit (90mg) or a cup of cooked broccoli (100mg) daily. Supplementation becomes most relevant when dietary consistency is low or during illness or heavy physical demand, providing a reliable daily intake that does not depend on what was available to eat on a particular shift.

Sources: WHO healthy diet guidance, EFSA water guidance, NCBI sleep stages, WHO stress guidance.

# Daily Nutrition

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