Vitamin and mineral supplements for preventing infections in older people

The number of older people is growing rapidly worldwide. In England alone the number of people older than 65 has more than doubled since the 1930s, and one fifth of the population is now aged 60 or more.¹ Ageing, disease, lifestyle, and environmental factors may all impair in older people the acquisition of food and its intake, processing, and metabolism, all leading to poor nutritional status.² Ageing is also associated with decreases in physical activity and lean body mass and an increase in body fat. The accompanying reductions in energy requirements and intake of food lead to lower intakes of macronutrients and micronutrients.²

Many older people exhibit poor immune responses and are at a high risk of infection.³ Although the mechanisms leading to the age related decline in innate and adaptive immunity are poorly understood, several studies have shown a beneficial effect on the immune system of supplementing vitamins A, C, and E, and zinc and selenium, singly and as multinutrient supplements.³

Yet most prospective trials have found no beneficial effects of multivitamin supplements on infection among healthy older people,⁴,⁵ and a recent meta-analysis of randomised controlled trials found the evidence for multivitamins and mineral supplements on risk of infections in older people to be weak and conflicting.⁶ Nevertheless, Girodon et al reported that supplementation with trace elements and vitamins reduced infections in institutionalised older people.⁷ Last year Meydani et al reported a protective effect of vitamin E supplementation over one year against infections of the upper respiratory tract, particularly the common cold, in elderly residents of nursing homes.⁸

Limitations

In this week's BMJ, Avenell et al report the results of a pragmatic, randomised, double blind, placebo controlled trial of daily supplements of multivitamins and minerals on morbidity from infections in people aged 65 and older (p 324).⁹ This study found that, in older people living at home, daily supplementation with multivitamins and multiminerals over one year had no beneficial effects on self reported infections, use of health services, or quality of life.

This was a robust study overall, and it largely confirms previous research. Having said that, all studies have their limitations, and the simplicity of the assessments in this trial by Avenell et al may have lead to confounding and measurement biases. For example, neither the researchers nor participants collected data on dietary intake or physical activity during the study period. And, although the trial design included a check of compliance with the supplements in a random 10% sample of participants, it did not include outcome data on biochemical status of vitamin and minerals. Two other important limitations, which the authors acknowledge, are the low doses of multivitamins and minerals used and the relatively healthy study population.

If trials of low dose supplementation show little or no benefit, might higher doses be more effective? Perhaps, but higher doses of such supplements in older people are not without risks. For instance higher doses of zinc and vitamin A supplements impair cellular immunity and the health of bones, respectively, among older people with vitamin D deficiency.²,¹⁰ Furthermore, the results of studies using doses that exceed recommended daily requirements for micronutrients cannot be readily translated into dietary guidelines. Few studies have attempted to modulate immune status in older people using foods or doses of nutrients that are realistically achievable through changing diet.¹¹

Holistic approach to diet

Diets of poor quality and quantity underlie and exacerbate many causes of major disease in older people and society as a whole including hypertension, type 2 diabetes, obesity, heart disease, stroke, cancer, mental ill health, and infections.¹² Evidence is increasing for a holistic approach to improving diet rather than focusing too closely on the effects of individual nutrients on risk factors and preventing disease. If combined with physical activity, which can increase appetite and enable a diet of marginal nutrient density to become adequate,¹² a better diet can make a substantial impact on population health, particularly of older people.

Supplements of vitamins and minerals might still benefit older people with increased risk of infections and those with evidence of vitamin deficiencies. But we will not know for sure until further robust studies have been done among high risk groups, including those with poor immunity and those living in institutional care.