The review conducted by BNF nutrition scientist, Dr Elisabeth Weichselbaum, found that while micronutrient deficiencies can impair the immune system, “insufficient evidence” exists demonstrating the cold-fighting capacity of supplementation.
The review found some data showed nutrients such as zinc and vitamin C could provide some benefits, but said more studies more needed to quantify the effects.
Supplementation was only deemed beneficial in population sub-groups such as elderly people, young children and pregnant women.
Weichselbaum’s findings are in alignment with the BNF position that all nutrients can be attained from a regular diet and that supplementation is largely unnecessary.
“Eating a healthy and varied diet with plenty of fruits and vegetables is the best way to ensure that daily vitamin and mineral requirements are met,” she concluded.
“A healthy diet will not prevent a common cold infection, but a sufficient nutrient supply will support the immune system and thus provides the best basis to lower the risk and duration of common cold infections.”
High dosage
Dr Robert Verkerk, the executive and scientific director at the Alliance for Natural Health International (ANH-I), said the BNF findings were to be expected.
“For example, the paper says the benefits of taking vitamin C are marginal, but it fails to say that nearly all studies have not included doses in excess of 2000 mg a day,” he said.
“In short, the paper tells us nothing new, and certainly fails to give people much needed information on how they might better manage upper respiratory infections such as common cold by using nutritional approaches, including the use of high dose supplements.”
Weichselbaum’s review – which also referenced vitamin E, vitamin A and iron – found that supplements could not only be costly, but high doses could block absorption of other nutrients. Zinc’s purported capacity to impair the uptake of iron was cited.
A copy of the review can be found here.
The review highlighted Department of Health reference nutrient intake (RNI) to support immune function that included 40mg/day for vitamin C; 600ug/day for vitamin A; 7mg/day for zinc; 14.8mg/day for iron and 60mg/day for selenium. All were achievable without supplementation.
In the case of vitamin C, Weichselbaum noted a Cochrane review of 30 trials with about 12 000 participants using doses of 200mg or higher.
“Vitamin C supplementation taken for prophylaxis reduced the duration of common cold symptoms by eight per cent in adults and by 13.6 per cent in children, but no effect was found when vitamin C was taken therapeutically,” she found, noting the authors had questioned the clinical usefulness of the findings.