Can Vitamin C Keep You Awake at Night?

December 11, 2025 •

3 min read

According to the National Institute for Health and Clinical Excellence (NICE), around a third of adults in Western countries experience sleep problems at least once a week. While many worry their vitamin C intake might be to blame, the truth is far more complex than this long-held misconception.

Quick Summary

This article explores whether vitamin C disrupts sleep, debunking the myth that it causes insomnia at regular doses while explaining how excessive intake can lead to indirect sleep issues.

Key Points

Normal doses don't cause insomnia: The idea that standard vitamin C intake keeps you awake is a myth stemming from an old, unproven claim.
Excessive intake can cause indirect issues: High doses (over 1000mg) can lead to side effects like heartburn and diarrhea, which may indirectly disturb sleep.
Vitamin C can support sleep: Adequate vitamin C levels are linked to better sleep quality, potentially by reducing oxidative stress and inflammation.
Optimal timing is morning or daytime: To maximize absorption and avoid potential GI discomfort before bed, taking vitamin C in the morning or splitting doses is recommended.
Body excretes excess: The body does not efficiently absorb mega-doses of vitamin C, and any excess is simply excreted, making high-dose supplements often wasteful.
Adequate levels matter: Lower vitamin C intake has been correlated with shorter sleep duration and more sleep disturbances, showing the importance of sufficient levels.

Debunking the Myth: The Truth About Vitamin C and Insomnia

The idea that vitamin C, or ascorbic acid, causes sleeplessness is a widespread belief, but it's largely a misconception. The origin of this myth can be traced back to a 1934 warning on supplement boxes suggesting against late-day intake due to a "slightly stimulating effect". However, this claim has never been substantiated by robust scientific evidence. In reality, adequate vitamin C levels are linked to better sleep quality, not worse. Several studies have even indicated that lower vitamin C intake is associated with shorter sleep duration and increased disturbances.

This positive association may be linked to vitamin C's antioxidant properties, helping to neutralize free radicals and reduce oxidative stress which can accumulate throughout the day. It may also support sleep by helping to regulate stress hormones like cortisol and aiding immune function. For most people, a standard daily dose of vitamin C will not negatively impact their sleep.

When Vitamin C Can Indirectly Affect Your Sleep

While normal doses are unlikely to cause sleeplessness, excessive intake—amounts typically over 1,000 to 2,000 mg per day—can cause side effects that indirectly interfere with sleep. The body's ability to absorb vitamin C is limited, and large doses can be inefficient and lead to gastrointestinal distress.

Potential High-Dose Side Effects

Gastrointestinal Issues: High doses may result in nausea, heartburn, cramps, bloating, and diarrhea. These can make it hard to sleep if experienced close to bedtime.
Minor Stimulation: Some individuals report a slight energizing effect from very high doses, potentially causing restlessness. This is not a common experience or a strong stimulant effect.
Other Side Effects: Though uncommon, excessive intake has been linked to headaches, fatigue, and an increased risk of kidney stones in susceptible individuals.

These issues are related to excessive intake rather than recommended daily amounts. The body will excrete large, unabsorbed doses.

How to Optimize Your Vitamin C Intake for Better Sleep

To maximize vitamin C benefits while minimizing sleep-disrupting side effects, timing and dosage are important.

Optimal Timing for Vitamin C

Morning or Daytime: Taking vitamin C in the morning or early afternoon is often suggested. This aligns with its role in supporting alertness.
Divided Doses: For higher daily intake, splitting the dose can improve absorption and reduce digestive upset.
With or After Food: Consuming vitamin C with a meal can help reduce GI issues, especially for those with sensitive stomachs.

Comparison: Normal vs. High Dosage of Vitamin C


Feature	Normal Dosage (75-90 mg/day for adults)	High Dosage (>1000-2000 mg/day)
Effect on Sleep	Supports better sleep quality.	Can indirectly disrupt sleep via digestive issues.
Absorption	Well-absorbed.	Inefficient; excess excreted.
Side Effects	Generally safe.	Possible GI discomfort, headaches, fatigue.
Best Practice	Take daily from diet/standard supplement.	Avoid mega-dosing unless advised by a doctor; split doses.

Conclusion

The myth that can vitamin C keep you awake at night is largely unfounded at recommended levels. Adequate vitamin C intake may actually improve sleep quality by reducing stress and supporting health. Sleep disruption is primarily a risk with excessive doses due to digestive side effects. Consuming a balanced diet rich in vitamin C and timing supplements appropriately can support sleep. For dietary guidelines, consult a source like the National Institutes of Health.

Frequently Asked Questions

For the vast majority of people, taking vitamin C at night will not keep you awake. The idea that it has a strong stimulating effect is a myth, and many studies suggest adequate intake is associated with better sleep.

Yes, excessive doses (over 1000-2000 mg) can cause side effects like gastrointestinal upset, heartburn, or diarrhea, which can indirectly interfere with your ability to sleep comfortably.

The best time is often in the morning or daytime. Taking it with a meal is recommended, especially for those with sensitive stomachs, to minimize potential digestive discomfort.

Research indicates that adequate vitamin C levels are linked to improved sleep quality, potentially due to its antioxidant properties and role in reducing oxidative stress. However, it is not a cure-all for severe sleep issues.

Yes, taking very high doses can lead to nausea, heartburn, diarrhea, and in rare cases, an increased risk of kidney stones. For most people, doses are safe within recommended limits.

The myth originated from a historical warning on supplements dating back to 1934, citing a 'slightly stimulating effect.' However, modern research has shown this claim to be unfounded, but the idea persists.

Some studies suggest that vitamin C, particularly in relation to iron absorption, may help alleviate symptoms of Restless Legs Syndrome (RLS), a condition that often disrupts sleep.

Getting vitamin C from a balanced diet rich in fruits and vegetables is generally preferable. Supplements are useful for filling nutritional gaps, but a food-first approach provides a wider array of nutrients.