Salt Intake and Hypertension - the plot thickens....

There is good evidence to support a connection between salt intake and population-based blood pressure levels. Excess dietary salt is associated with increased blood pressure in individuals. It has also been argued that like the effects of restraining tobacco consumption there would also be a salutary effect on population outcomes if salt intake was constrained. A recent article in the June 12 issue of CMAJ by Elizabeth Dunford and colleagues is a must-read because of it's practical importance.

Basically, Dunford and co-workers performed a survey assessing the salt content of food items sold by 6 trans-national food companies operating in the US, Australia, Canada, France, New Zealand, and the UK. They calculated mean salt content and compared these within and between countries and companies. The companies involved were: Burger King (known as Hungry Jack’s in Australia), Domino’s Pizza, Kentucky Fried Chicken, McDonald’s, Pizza Hut and Subway.

Their main findings were:

1. Substantial variation in the mean salt content for different categories of products. For example, the salads in the survey contained 0.5 g of salt per 100 g, whereas the chicken products contained 1.6 g. Large serving sizes meant that some burger and chicken products had >6 g of salt per serving, some salads had >7 g, the saltiest sandwiches had 8 g, and one particular pizza had >10 g of salt.

2. Marked variability between countries: chicken products from the UK contained 1.1 g of salt per 100 g, whereas chicken products from the US contained 1.8 g. For example, the mean salt content per 100 g for savory breakfast items was significantly lower in the UK (1.4 g), Australia (1.3 g) and New Zealand (1.1 g) than in the US (1.8 g) (all p < 0.001), and chicken products in the UK were significantly lower in salt (1.1 g salt per 100 g) than in the US (1.8 g) (p < 0.001).

3. The mean salt content of food categories varied between companies and between the same products in different countries, for example, McDonald’s Chicken McNuggets contained 0.6 g of salt per 100 g in the UK, but 1.6 g of salt per 100 g in the US. As well, the mean salt level in sandwiches was 70% higher in Pizza Hut products than in Subway (p < 0.001).

The authors conclude: "Decreasing salt in fast foods would appear to be technically feasible and is likely to produce important gains in population health — the mean salt levels of fast foods are high, and these foods are eaten often. Governments setting and enforcing salt targets for industry would provide a level playing field, and no company could gain a commercial advantage by using high levels of salt."

The other practical point, of course, is that when we see patients with CKD who invariably have hypertension that is difficult to control, we should educate them about salt content in fast food items and how much variability there currently is.