Are the UK's vitamin C recommendations evidence-based? A critical comment.

The UK vitamin C recommendation of 40 mg/d for adults was established in 1991 and based on a 1953 Sheffield study.

• The 1953 Sheffield study found that 10 mg/d prevents scurvy.
• The 40 mg/d level was chosen for yielding 'somewhat higher plasma levels' above the scurvy-prevention threshold.
• The UK recommendation has not been updated since 1991.
• The USA recommendation is higher, at 90 mg/d for men and 75 mg/d for women, reflecting substantial international variation in recommended intake levels.

At least six controlled trials published before 1991 reported benefits from vitamin C supplementation in participants whose baseline vitamin C intake was already 40 mg/d or higher.

• These trials were available at the time the UK recommendation was established in 1991 but were overlooked.
• The findings suggest that 40 mg/d may not be sufficient to maintain full health, even when it prevents clinical scurvy.
• The authors argue these trials represent 'key evidence' that should have informed the UK recommendation.

One randomised controlled trial published in 1993 found benefits from vitamin C supplementation at a baseline intake of approximately 500 mg/d.

• This trial involved ultramarathon runners, and the authors note 'the findings should not be broadly generalised.'
• The result challenges the assumption that 40 mg/d is universally adequate to maintain full health.
• The trial was published after the 1991 UK recommendation was established.

The UK recommendations were narrowly focused on preventing dermatological symptoms of scurvy, despite evidence that vitamin C deficiency can cause cardiac dysfunction and greater morbidity due to respiratory infections.

• Evidence of cardiac dysfunction and respiratory infection morbidity associated with vitamin C deficiency was available 'even at the time' of the 1991 recommendation.
• The authors characterize this narrow focus on dermatological scurvy symptoms as a limitation of the UK recommendation process.
• The commentary argues broader clinical outcomes should be considered in setting vitamin C recommendations.

The authors conclude that the current UK vitamin C recommendation should be re-evaluated in light of controlled trial evidence and broader clinical outcomes.

• The recommendation has remained at 40 mg/d since 1991, making it lower than recommendations in the USA and reflecting substantial international variation.
• The authors argue the recommendation overlooked 'key evidence available at the time.'
• Re-evaluation should consider both controlled trial evidence and outcomes beyond prevention of dermatological scurvy symptoms.