Does vitamin C prevent you from sleeping?

Supposed to help us fight fatigue and give us energy, can vitamin C disrupt sleep when taken at the end of the day? How does it work and what are its properties? Is it really not recommended to take it in the evening? The answers of Dr Jonathan Taïeb, sleep doctor.

Vitamin C: what are its properties?

From its chemical name ascorbic acid , vitamin C is a water-soluble vitamin which is involved in many functions in the body. “It is a powerful antioxidant, which plays, among other things, a role in supporting the immune system. It helps strengthen the body's defenses and fight against infections,” says Dr. Taïeb. Among its other features, vitamin C stimulates the synthesis of collagen - a protein essential to the structure of skin, bones, cartilage and blood vessels - making it useful in healing wounds and maintaining health. tissue integrity. And finally, it promotes the absorption of non-heme iron (from plants) in the intestine, which makes it particularly interesting for people suffering from iron deficiency anemia.

How long does vitamin C work for?

Vitamin C is water soluble, meaning it is soluble in water. Once ingested, it is quickly absorbed by the small intestine and enters the bloodstream. It is then used by the body for various functions: synthesis of collagen, protection against free radicals and support of the immune system... After having fulfilled these functions, the unused vitamin C is excreted by the kidneys in the urine: it does not remain therefore not long in the body.
The half-life of vitamin C – the time it takes for its concentration in the blood to drop by half – is around 2 to 3 hours in healthy people, which is relatively short.

What are the disadvantages of vitamin C for sleep?

The belief that vitamin C might prevent you from sleeping well has never been scientifically substantiated.

This belief is a myth: vitamin C has no harmful effects on sleep. Dr Taïeb, sleep doctor. 

Conversely, several studies suggest that this water-soluble vitamin could even have some beneficial effects on sleep  !
First of all, its powerful  antioxidant  action makes it effective in fighting free radicals responsible for oxidative stress and premature aging of cells. However, according to a study carried out in 2018, this oxidative stress could precisely be the cause of sleep disorders. (1)

A systematic review based on 4 studies examining the impact of vitamin C on sleep quality found that people with higher levels of vitamin C in their diet had better sleep quality than those who had less. (2)

It would also help to reduce the level of cortisol - or stress hormone - which would have a positive effect on stress and promote restorative sleep.

Finally, vitamin C is thought to play a role in the production of serotonin , a neurotransmitter precursor to melatonin , known as the sleep hormone. Based on the principle that a lack of serotonin in the body could promote sleep disorders, vitamin C could therefore contribute to better quality sleep thanks to its action on the production of serotonin and indirectly melatonin.

Can you take vitamin C in the evening before sleeping, or rather in the morning?

The idea that it would be better to avoid taking vitamin C at the end of the day is not new. Specifically, it follows the instructions for the first vitamin C supplement marketed in 1934 by the Swiss pharmaceutical laboratory Roche, which states: “It is preferable not to take this medication at the end of the day because of its slightly stimulating effect. . » This mention was added because of the participation of vitamin C in the synthesis of dopamine, a chemical messenger of the brain involved in wakefulness and vigilance. However, the few studies carried out, first on rats, then on healthy human volunteers who took high doses of vitamin C before bed, showed no change in the sleep cycle .

However, it cannot be ruled out that some particularly sensitive people may experience difficulty falling asleep when taking vitamin supplements at the end of the day. If in doubt, vitamin C supplements can be taken in the morning or midday. Dr Taïeb

Likewise, all fruits rich in vitamin C , such as citrus fruits or even kiwis , can be taken at dinner. “A 2023 study published by the scientific journal Nutrients (3), carried out for 4 weeks on athletes who consumed two kiwis daily 1 hour before bed , observed a notable improvement in the quality of sleep , an increase in the total duration sleep, and a reduction in nighttime awakenings and stress,” adds Dr. Taïeb.