Sodium in New Zealand: intake, consumer perceptions, and implications for chronic disease

Abstract

Sodium is widely used in foods to enhance flavour, preserve, and improve processing. Although sodium is an essential nutrient, the majority of the world’s population consumes in excess of what is required, and more than recommended dietary guidelines. Dietary sodium reduction has the potential to substantially reduce mortality and morbidity from cardiovascular disease (particularly stroke and ischaemic heart disease) and reduce health care costs. Sodium risk management strategies have been identified as some of the most effective and cost effective public health strategies available for reducing chronic disease. This thesis reviews relevant literature and describes five studies designed to inform New Zealand policymakers regarding an appropriate risk reduction strategy.

A qualitative study of a convenience sample of 16 adult grocery shoppers showed New Zealand consumers lack the background knowledge necessary to understand and regulate their own salt intake. Furthermore, they were unable to interpret existing food labels with respect to dietary salt. An on-line experiment in which around 700 participants viewed varied nutrition label formats indicated that the addition of a front-of-pack label, particularly those with simple visual cues (such as the multiple traffic light label) enhanced consumers' ability to discriminate between high and low sodium products. This ability persisted even when those products featured potentially misleading nutrition claims.

Twenty-four hour urinary sodium excretion is widely considered the ‘gold standard’ for estimation of population sodium intake. The potential to use spot urine measurements, as a surrogate for 24-hour urinary sodium was estimated by analysing the relationship between spot and 24-hour urinary sodium excretion using three published formulae (a formula proposed by the Pan American Health Organization, and two formulae derived in Japanese populations: by Tanaka and Kawasaki) in a convenience sample of 100 healthy volunteers. Spot urine sampling was found to be a suitable alternative to 24-hour urine collection in population surveys when results are converted into estimates of 24-hour sodium excretion using the formula proposed by the Pan American Health Organization.

Spot urine results from New Zealand Adult Nutrition Survey showed that New Zealand adult population sodium intake was substantially higher than that recommended in dietary guidelines, with 65% of adults having an intake higher than the recommended upper level of intake of 2300mg/day. Mean adult sodium intake excretion was 3544 mg; 4013mg for men and 3115 mg for women. Sodium intake was significantly higher in men, those aged 19-44 years, and people who reported ‘regularly’ or ‘always’ adding salt to cooked food after it has been cooked or prepared.

Blood pressure results from the 2008/09 New Zealand Adult Nutrition Survey showed that mean systolic blood pressure has increased since 2002/03 for New Zealand European and Others aged 35-54 years and Māori aged 35-74 years, reversing a downward trend observed in New Zealand European and Others between 1982 and 2002.

A population sodium reduction strategy is warranted which should follow international best practice include both changes in the food supply, as well as demand orientated initiatives such as consumer education and improvements in food labelling and advice to consumers to add less salt to food in the home.