Post-prandial syncope due to nitrates in food

Vascular effects of dietary nitrate (as found in green leafy vegetables and beetroot) via the nitrate-nitrite-nitric oxide pathway

The discovery that dietary (inorganic) nitrate has important vascular effects came from the relatively recent realization of the 'nitrate-nitrite-nitric oxide (NO) pathway'. Dietary nitrate has been demonstrated to have a range of beneficial vascular effects, including reducing blood pressure, inhibiting platelet aggregation, preserving or improving endothelial dysfunction, enhancing exercise performance in healthy individuals and patients with peripheral arterial disease. Pre-clinical studies with nitrate or nitrite also show the potential to protect against ischaemia-reperfusion injury and reduce arterial stiffness, inflammation and intimal thickness. However, there is a need for good evidence for hard endpoints beyond epidemiological studies. Whilst these suggest reduction in cardiovascular risk with diets high in nitrate-rich vegetables (such as a Mediterranean diet), others have suggested possible small positive and negative associations with dietary nitrate and cancer, but these remain unproven. Interactions with other nutrients, such as vitamin C, polyphenols and fatty acids may enhance or inhibit these effects. In order to provide simple guidance on nitrate intake from different vegetables, we have developed the Nitrate 'Veg-Table' with 'Nitrate Units' [each unit being 1 mmol of nitrate (62 mg)] to achieve a nitrate intake that is likely to be sufficient to derive benefit, but also to minimize the risk of potential side effects from excessive ingestion, given the current available evidence. The lack of data concerning the long term effects of dietary nitrate is a limitation, and this will need to be addressed in future trials.

Nitrate anaphylaxis

BACKGROUND

Nitrate and nitrite salts are commonly used to preserve and sustain color in a number of processed meats. To date there have been no described cases of anaphylaxis to either nitrates or nitrites in the literature.

OBJECTIVE

We report a patient with anaphylaxis to nitrates and nitrites documented by double-blind, placebo-controlled capsule challenge.

METHODS

A 22-year-old previously well male, presented to a tertiary referral center with a 4-year history of recurrent anaphylaxis after eating take-out food. No further episodes occurred while adhering to a strict elimination diet. We performed a double-blind, placebo-controlled capsule challenge both with food substances and starch placebo. These occurred in a hospital setting with full resuscitative procedures available.

RESULTS

An acute anaphylactic reaction occurred following a challenge to nitrates and nitrites. Generalized allergic reactions were observed on separate occasions following administration of artificial colorings and metabisulfite. There was a mild urticarial reaction following salicylates. He was placed on a diet free of sulfites, nitrates, nitrites, and low in salicylates and he has had no further reactions. A computer based search of the Medline, Current Contents and EMBASE databases found no previously reported cases of urticaria, angioedema, or anaphylaxis to either nitrates or nitrites.

CONCLUSION

The ingestion of processed meats containing nitrate or nitrite salts may be associated with angioedema and anaphylaxis and should be considered when investigating patients with suspected food allergy.