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The public needs more help to get rid of its blind spot about salt, especially the great danger of weaning infants with salty foods.

DANGER TO INFANTS

After the death of a 3-month-old infant in England, the inquest heard evidence from two consultant paediatricians at the Sheffield Children's Hospital that the cause of death was acute hypernatraemia due to inappropriate weaning on adult foods. The child had eaten instant mashed potatoes and gravy, both made from commercial packets, with no salt added by the mother.

Salt Matters (page 167) summarises the interesting press coverage at the inquest. Professional journals ignored this (the danger of salt to infants is not medical news). It is seldom fatal, but hypernatraemia should be high on the list in the differential diagnosis of unexplained illness at weaning time. Mothers who mash home-cooked vegetables for the baby must eliminate added salt completely and never check the taste in the mistaken belief that salt would make weaning easier (salt makes it more difficult).

DEFINITION OF GOOD SALT CONTROL IN ADULTS

The Menzies Institute measures the salt intake of adult referrals with 24-hour urine collections and defines good salt control as sodium excretion below 50 mmol/d for men and 40 mmol/d for women -- results seen when complying with the Australian dietary guidelines. Note that international (SI) units for sodium are millimoles (abbreviated mmol), and 1 mmol = 23 mg.

Patients referred to the Menzies Institute compare their baseline and follow-up results with data from a dietary survey [1]. Out of 194 people in this survey all but one told us their diet was 'normal', but their sodium excretion varied between 26 and 337 mmol/day, as plotted here with a log x-axis:

Sodium intake during human evolution could not have exceeded 30 mmol/d [2] and the huge variation in modern diets occurs when salty processed foods are eaten without checking the sodium content. Food labels (not yet converted to mmol) reveal sodium contents between 1 mg/100g and over 9000 mg/100g. Breast milk has only 14 mg/100g, meat and fish up to 80 mg/100g. Common salt (39% sodium) has 39 000 mg/100g, so even small amounts distort the electrolyte balance. The amount added to the typical Western diet inverts the sodium-potassium ratio, actively contributing to many chronic 'diseases of civilization' [3].

The Tolerable Upper Limit (UL) for sodium

No country sets the UL for sodium above 100 mmol/d.  In Australia the UL is still 100 mmol/d, where it has been since 1984, but there is a Suggested Dietary Target of 70 mmol/day "to prevent chronic disease" which really makes the UL irrelevant.

FEASIBILITY OF GOOD SALT CONTROL

In Australia the book Salt Matters makes it both feasible and enjoyable by explaining  how to follow the simple guideline to choose low salt foods. Fresh foods make is easy but processed foods are stilll making it difficult, as low salt processed foods are still scarce.  The food industry needs to make it easier in shops and restaurants, and the key to that is consumer demand.

The US government recommends 65 mmol/d (1500 mg/d) to all Americans [4] and calls on the food industry to cater for it. A market that eventually makes 65 mmol/d feasible for a population of 300 million can surely make 40-50 mmol/d easy for motivated patients. The DASH-Sodium study compared three levels of sodium excretion and found the lowest (65 mmol or 1500 mg) had the greatest effect on blood pressure, both in hypertension and prehypertension (BP =120/80 and <140.90) [5]. Controlling prehypertension prevents hypertension, which is why 65 mmol/d is the government's goal for all Americans [4].

References

1. Beard TC, Woodward DR, Ball PJ, Hornsby H, von Witt RJ, Dwyer T. The Hobart Salt Study 1995: few meet national sodium intake target. Medical Journal of Australia 1997;166:404-07.

2. Eaton SB, Konner MJ. Paleolithic nutrition: a consideration of its nature and current implications. N Engl J Med 1985;312:283-89.

3. Cordain L, Eaton SB, Sebastion A, Mann N, Lindeberg S, Watkins BA, O'Keefe JH, Brand-Miller J. Origins and evolution of the Western diet: health implications for the 21st century. American Journal of Clinical Nutrition 2005;81:341-54.

4. www.nhlbi.nih.gov/new/press/may17-00.htm . (accessed 9 January 2005).

5. Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA, Harsha D, et al. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. New England Journal of Medicine 2001;344:3-10.


Page last modified on: Friday 07 Nov, 2008

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