Micronutrients in adult nutritional support: requirements and benefits

Limited effects of micronutrient supplementation on strength and physical function after abdominal aortic aneurysmectomy

BACKGROUND

Tissue injury following ischemia-reperfusion is mediated in part by free oxygen radicals. We hypothesized that perioperative micronutrient supplementation would augment antioxidant defenses, minimize muscle injury, and minimize postoperative decreases in muscle strength and physical function following abdominal aortic aneurysmectomy.

SETTING

A university-affiliated hospital and regional referral center.

DESIGN

A randomized, double-blind, placebo-controlled trial of supplementation with beta-carotene, vitamins C and E, zinc, and selenium for a period of 2-3 weeks prior to surgery and 1 week thereafter.

STUDY POPULATION

Patients undergoing elective abdominal aortic aneurysmectomy (n=18 per group).

PRINCIPAL MEASUREMENTS

Handgrip and other measures of strength and physical function.

RESULTS

Handgrip and quadriceps strength decreased following surgery, but not to a significantly different extent in the placebo and supplemented groups. Self-rated physical function decreased following surgery in the placebo group and was preserved in the supplemented group.

CONCLUSIONS

Perioperative supplementation with micronutrients with antioxidant properties has limited effects on strength and physical function following major elective surgery.

Protein-energy undernutrition in hospital in-patients

Impaired nutritional status has been frequently reported in surveys estimating its prevalence amongst patients in hospital. While there is no doubt that protein-energy undernutrition has serious implications for health, recovery from illness or surgery and hospital costs, lack of nationally or internationally accepted cut-off points and guidelines for most nutrition-related variables make nutritional assessment difficult and proper comparisons between studies impossible. In reviewing published work in which the prevalence of undernutrition has been assessed, it can be seen that each study defined undernutrition, or nutritional risk, using different methodology. This present review aims to highlight the problems which arise when deciphering these studies, and the resulting difficulty in determining the true prevalence of undernutrition and nutritional risk, amongst both general and specific groups of hospital in-patients. It is widely agreed that routine hospital practices can further adversely affect the nutritional status of sick patients in hospital. How this occurs, and the potential effects of impaired nutritional status on clinical outcome are examined. The methods currently available to assess nutritional status are evaluated in the knowledge that such assessments are difficult in clinical practice. The review concludes by proposing that if we want the medical and nursing professions to consider the nutritional status of hospital patients seriously, definitions of undernutrition and nutritional risk, and cut-off values for the nutritional variables measured must be agreed to allow evidence-based practice. Outcome measures which allow clear comparisons between groups and treatments must be used in studies assessing the effects of nutritional interventions.

Technical aspects of trace element supplementation

Routine supplementation of total parenteral nutrition mixtures with the readily available single or combination trace elements products is becoming more widespread. As more is learned about deficiency syndromes and monitoring techniques, so too must we understand more about the physicochemical interactions between individual trace elements and other nutrients, that could ultimately affect bioavailability. Expert pharmaceutical assessment of these complex reactions, that have been demonstrated to occur in solution, becomes increasingly important in order to optimize the efficacy of micronutrient therapy.

Assessment of status

Laboratory methods for the measurement of micronutrients are usually based upon determinations in the peripheral blood. Most are relatively insensitive, but can screen for impending acute deficiency or toxicity. The metabolic responses to disease, injury and infection may alter the laboratory findings independently of dietary supply. Methods based upon the intra-cellular biochemical function of individual micronutrients are becoming available and can detect more marginal deficiencies. The investigation of general populations for micronutrient depletions largely relies upon clinical and epidemiological evaluation of responses to controlled trials of supplementation.