Bleeding tendency and low vitamin C requirements — US meta-analysis

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Gingival bleeding tendency and also retinal haemorrhaging were associated with low vitamin C levels in the bloodstream, found a US meta-analysis.

And if someone is on a specialised diet, such as a paleo diet, it's important that they take a look at their vitamin C intake, the study authors said. "Vitamin C-rich fruits such as kiwis or oranges are rich in sugar and thus typically eliminated from a low-carb diet."

Current advice from the America Dental Association tells you that if your gums bleed, make sure you are brushing and flossing twice a day because it could be a sign of gingivitis, an early stage of periodontal disease. However, a University of Washington study suggests you should also check your intake of vitamin C.

"When you see your gums bleed, the first thing you should think about is not, I should brush more. You should try to figure out why your gums are bleeding. And vitamin C deficiency is one possible reason," said the study's lead author Philippe Hujoel, a practicing dentist and professor of oral health sciences in the UW School of Dentistry.

Hujoel's study analysed published studies of 15 clinical trials in six countries, involving 1,140 predominantly healthy participants, and data from 8,210 US residents surveyed in the Centres for Disease Control and Prevention's Health and Nutrition Examination Survey. The results showed that bleeding of the gums on gentle probing, or gingival bleeding tendency, and also bleeding in the eye, or retinal haemorrhaging, were associated with low vitamin C levels in the bloodstream. And, the researchers found that increasing daily intake of vitamin C in those people with low vitamin C plasma levels helped to reverse these bleeding issues.

Of potential relevance, says Hujoel, who is also an adjunct professor of epidemiology in the UW School of Public Health, both a gum bleeding tendency and retinal bleeding could be a sign of general trouble in one's microvascular system, of a microvascular bleeding tendency in the brain, heart and kidneys.

The study does not imply that successful reversing of an increased gingival bleeding tendency with vitamin C will prevent strokes or other serious health outcomes, Hujoel stresses. However, the results do suggest that vitamin C recommendations designed primarily to protect against scurvy – a deadly disease caused by extremely low vitamin C levels – are too low, and that such a low vitamin C intake can lead to a bleeding tendency, which should not be treated with dental floss.

Consequently, Hujoel does recommend people attempt to keep an eye on their vitamin C intake through incorporation of non-processed foods such as kale, peppers or kiwis into your diet, and if you can't find palatable foods rich in vitamin C to consider a supplement of about 100 to 200 milligrams a day.

People who exclusively eat lean meats and avoid offal, the vitamin-rich organ meats, may be at a particularly high risk for a low vitamin C intake. The association between gum bleeding and vitamin C levels was recognized more than 30 years ago. In fact, two studies co-authored by former dean of the UW School of Dentistry Paul Robertson (published in 1986 and 1991) identified gum bleeding as a biological marker for vitamin C levels.

However, this connection somehow got lost in dental conversations around bleeding gums.

"There was a time in the past when gingival bleeding was more generally considered to be a potential marker for a lack of vitamin C. But over time, that's been drowned out or marginalised by this over-attention to treating the symptom of bleeding with brushing or flossing, rather than treating the cause," Hujoel said.

Hujoel's literature review also determined that "retinal haemorrhaging and cerebral strokes are associated with increased gingival bleeding tendency, and that (vitamin C) supplementation reverses the retinal bleeding associated with low (vitamin C) plasma levels."

So, missing the possible connection between gum bleeding and low levels of vitamin C has the potential to have serious health consequences.

The study authors write: "A default prescription of oral hygiene and other periodontal interventions to 'treat' microvascular pathologies, even if partially effective in reversing gingival bleeding as suggested in this meta-analysis, is risky because it does not address any potential morbidity and mortality associated with the systemic microvascular-related pathologies."


Study details
Bleeding tendency and ascorbic acid requirements: systematic review and meta-analysis of clinical trials

Philippe P Hujoel, Tomotaka Kato, Isabel A Hujoel, Margaux L A Hujoel

Published in Nutrition Reviews on 1 February 2021

The World Health Organization set the recommended daily vitamin C intake, henceforth referred to as ascorbic acid (AA), on the basis of scurvy prevention. Double-blind AA depletion-repletion studies suggest that this recommended AA dose may be too low to prevent microvascular fragility.
(1) To conduct a systematic review and meta-analysis of controlled clinical trials on whether AA supplementation leads to a reduced gingival bleeding tendency, a manifestation of microvascular fragility; and (2) to relate AA plasma levels to retinal hemorrhaging, another manifestation of microvascular fragility.
Data sources
Data were reviewed from 15 trials conducted in 6 countries with 1140 predominantly healthy participants with measures of gingival bleeding tendency, and from the National Health and Nutrition Examination Survey (NHANES) III of 8210 US residents with measures of retinal hemorrhaging.
In clinical trials, AA supplementation reduced gingival bleeding tendency when estimated baseline AA plasma levels were < 28 μmol/L (standardized mean difference [SMD], −0.83; 95%CI, −1.16 to −0.49; P < 0.002). Supplementation with AA did not unequivocally reduce gingival bleeding tendency when baseline estimated AA plasma levels were >48  μmol/L or unknown (respective standardized mean differences: −0.23, 95%CI, −0.45 to −0.01, P < 0.05; and −0.56; 95%CI: −1.19 to 0.06, P < 0.08). In NHANES III, prevalence of both retinal hemorrhaging and gingival bleeding tendency increased when AA plasma levels were within the range that protects against scurvy (11–28 μmol/L; respective prevalence ratios adjusted for age and sex: 1.47; 95%CI: 1.22–1.77; and 1.64; 95%CI: 1.32–2.03; P < 0.001 for both).
Consistent evidence from controlled clinical trials indicates that setting human AA requirements based on scurvy prevention leads to AA plasma levels that may be too low to prevent an increased gingival bleeding tendency. Gingival bleeding tendency and retinal hemorrhaging coincide with low AA plasma levels and thus may be reflective of a systemic microvascular pathology that is reversible with an increased daily AA intake.


University of Washington material


Nutrition Reviews study (Restricted access)



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