How does salt affect children?

Introduction

It is well known a that a high salt intake is associated with high blood pressure in the adult population.  There is now evidence to show that a high salt intake in children also influences blood pressure and may predispose an individual to the development of a number of diseases including: high blood pressure, osteoporosis, respiratory illnesses such as asthma, stomach cancer and obesity.

Furthermore, there is evidence that dietary habits in childhood and adolescence also influence eating patterns in later life. Liking salt and salty foods is a learned taste preference and the recommendation that the adult population reduce their sodium intake will be more successful if children do not develop a preference for salt in the fist place. This can only be achieved if children are given a diet which is low in salt.(1-2)

Dietary Recommendations

Like adults, children consume more salt than the maximum recommendation (3) (Fig. 1). Simple measures need to be taken to help reduce salt intake and therefore reduce the number of people suffering from cardiovascular disease.

Simple changes can be made to a child’s diet to make sure they don’t consume too much salt. Giving them healthy snacks such as fruit and yogurt rather than crisps, swapping ham and cheese sandwiches for chicken or tuna, never adding salt to their food and checking labels of products such as sauces, bread and cereal can all help to reduce the salt intake of children.When cooking for children of all ages do not add salt to their food and discourage them from adding salt at the table. Habits formed in childhood continue through to adulthood so give your children a good start by reducing their salt intake today.

AgeMaximum Salt Intake
0-6 months<1g / day
6-12 months1g / day
1-3 years2g / day
4-6 years3g / day
7-10 years5g / day
11 years and above6g / day

Fig1: SACN Recommended maximum salt intakes

Babies

Babies only need very small amounts of salt and their kidneys are too immature to cope with any added salt. Therefore salt should never be added to any food that is cooked for your baby. Breast milk naturally meets all of a baby’s nutritional requirements, including a tiny amount of salt and infant formula is specially formulated to contain the right amount of salt. It is always important to make up formula milk correctly to the manufacturers instructions.

Weaning

During weaning, no salt should be added to any foods. Weaning products do not have any added salt and on tasting them you may find they taste bland, but do not add any salt.  Do not add any salt when preparing weaning foods and limit the amount of high salt foods that your child eats. Also avoid using processed foods that are not made specifically for babies such as cooking sauces as these can be high in added salt.

Children

Once your child is eating the same foods as the rest of the family it is important to continue not adding any salt to their food. This will also benefit the rest of the family! It is at this point that children’s salt intake tends to increase dramatically due to eating higher salt foods.
Homemade meals cooked using fresh ingredients are naturally lower in salt than convenience meals and processed food. Limit foods that are high in salt, and always check nutritional
information, even on products aimed at children, and choose those with less salt. A low salt diet throughout childhood will help prevent children developing a taste for salty foods and reduce the likelihood of them eating a diet high in salt during adulthood.

Teenagers

Teenagers should be warned to limit their consumption of salty savoury and sweet snacks such as crisps, chips, supermarket bought biscuits and cake slices; and takeaway foods such as chicken nuggets, pizza and burgers which can greatly increase their salt intake.

Blood pressure

A high salt intake has been shown to increase blood pressure and this increases the risk of heart disease and strokes three fold. There is evidence that a high salt diet in childhood can increase blood pressure and thus increase the risk of cardiovascular disease (Fig. 2). There is also evidence that a modest reduction in salt intake to the current age specific recommendations will reduce blood pressure and the age associated rise in blood pressure later in life. In the long term this reduction will significantly reduce the number of people affected by cardiovascular disease.

The National Diet and Nutrition Survey (NDNS) showed that use of salt at the table for both boys and girls and the use of salt in cooking for girls were associated with increased systolic blood pressure.(5) In a Dutch study blood pressures of over 200 children (mean age 13 years) were measured along with urinary sodium and potassium concentrations and then re-measured yearly over six years. A larger rise in blood pressure was associated with lower urinary potassium or higher sodium/potassium ratios.(6) This suggests that both dietary potassium and dietary sodium are related to the rise in blood pressure in childhood and may be important in the early pathogenesis of primary hypertension.

Figure 2. The relation of salt excretion to the slope of the rise in systolic blood pressure with age in 52 centres in the INTERSALT study. 

Osteoporosis

A high salt intake can cause calcium losses through the urine which can lead to bone demineralisation and significantly increase the risk of osteoporosis, a bone condition causing fragility and breakage's. Although osteoporosis is most common amongst older people, studies have shown that the effect of salt on calcium metabolism can be detected in children and continue in to adult life.(9) This increases the risk of osteoporosis later in life, particularly for girls.  

One study has found that for every 100mmol increase in salt intake, urinary Ca is increased by 1.4mmol.(10,11) Assuming that this loss is from the bones, it equates to about 1% extra loss of bone each year.(12) Both epidemiological studies and randomised trials have shown that a decrease in salt intake reduces urinary calcium excretion.  

There is evidence that at the time when girls are reaching puberty and increasing bone mass to reach their peak bone mass (PBM), their diet is deficient in potassium and calcium.(2) Coupled with the high salt intake of this age group, you have many of the elements which lead to a lower PBM being achieved, which later in life predisposes that individual to an increased risk of osteoporosis.

Controlled trials demonstrate that a reduction in salt intake does lower blood pressure in children. For example, the first ever meta-analysis of controlled salt reduction trials in children, demonstrates that reducing children's salt intake by half results in immediate falls (1.2 mmHg systolic and 1.3 mmHg diastolic in children 8-16yrs) in blood pressure. The meta-analysis looks at the combined results of ten trials studying a total of 966 children and adolescents aged between 8 and 16.7 These reductions are extremely significant at a population level. For example, previous studies have suggested that a 2-3mmHg reduction in systolic blood pressure across the whole UK population would confer more benefit than all of the blood pressure treatment tablets that are currently being prescribed.(8)

Obesity

Figure 3 – Relationship between salt intake and fluid consumption in children and adolescents. (2)

Whilst salt is not a direct cause of obesity it is a major influencing factor through its effect on soft drink consumption.  Salt makes you thirsty and increases the amount of fluid you drink. 31% of the fluid drunk by 4-18 year olds is sugary soft drinks13 which have been shown to be related to childhood obesity (Fig.3).(14,15) 

It has been estimated that a reduction in salt intake from 10 g/d to the WHO recommended level of 5 g/d would reduce fluid consumption by about 350 mL/day. A study which analysed the sales of salt and carbonated beverages in the USA between 1985 and 2005 showed a close link between the two, as well as a parallel link with obesity.(16)

An analysis of the NDNS for young people (4 – 18years) showed salt intake was associated with both fluid intake and sugar-sweetened soft drink consumption.(13)  A reduction in salt intake by 1 g/d was found to be associated with a difference of 100g/day in total fluid and 27 g/d in sugar-sweetened soft drinks. This demonstrates that salt intake is an important determinant of total fluid and sugar-sweetened soft drink consumption in children. Reducing salt intake could therefore be important in reversing the current trend of increasing childhood obesity.

Other conditions

A high salt diet during childhood could increase the risk of other conditions later in life. This includes increasing the risk of stomach cancer by damaging the stomach lining and increasing the growth of the bacteria Helicobacter pylori;(17,18) asthma by increasing bronchial reactivity; kidney disease by increasing protein urea (major kidney disease risk factor) and the stress the kidney is under.(19)

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References

1. Hofman, A., A. Hazebroek, and H.A. Valkenburg, A randomized trial of sodium intake and blood pressure in newborn infants. Jama, 1983. 250(3): p. 370-3.
2. Geleijnse, J.M., et al., Long-term effects of neonatal sodium restriction on blood pressure. Hypertension, 1997. 29(4): p. 913-7.
3. Scientific Advisory Committee on Nutrition, Salt and health. 2003. The Stationery Office. Available at http://www.sacn.gov.uk/pdfs/sacn_salt_final.pdf . Accessed March 22, 2005.
4. NDNS 09/09
5. Gregory J, L.S., Bates CJ, Prentice A, Jackson L, Smithers G, Wenlock R, Farron M., National Diet and Nutrition Survey: young people aged 4 to 18 years. Vol. 1: Report of the diet and nutrition survey. 2000, London: The Stationery Office. 271-336.
6. Geleijnse, J.M., D.E. Grobbee, and A. Hofman, Sodium and potassium intake and blood pressure change in childhood. Bmj, 1990. 300(6729): p. 899-902.
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8. Rose, G., Strategy of prevention: lessons from cardiovascular disease. Br Med J (Clin Res Ed), 1981. 282(6279): p. 1847-51.
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10. Ho SC et al. Sodium is the leading dietary factor associated with urinary calcium excretion in Hong Kong Chinese adults. Osteoporosis International. 2001; 12, 723-731
11. Nordin CBE et al. The nature and significance of the relationship between urinary sodium and urinary calcium in women. The Journal of Nutrition. 1993; 123,1615-1622
12. Evans CEL et al. The effect of dietary sodium on calcium metabolism in premenopausal and postmenopausal women. European Journal of Clinical Nutrition. 1997; 51,394-399
13. He FJ et al. Salt Intake Is Related to Soft Drink Consumption in Children and Adolescents: A Link to Obesity?  Hypertension. 2008; 51, 629-634
14. Ludwig DS et al. Relation Between Consumption of Sugar-sweetened Drinks and Childhood Obesity: a prospective, observational analysis. Lancet. 2001; 357, 505-508,
15. James J et al.  Preventing Childhood Obesity by Reducing Consumption of Carbonated Drinks: Cluster Randomised Controlled Trial. British Medical Journal. 2004; 328,1237
16. Karppanen H, Mervaala E: Sodium Intake and Hypertension. Prog Cardiovasc Dis. 2006; 49, 59-75
17. Tsugane, S., et al., Salt and salted food intake and subsequent risk of gastric cancer among middle-aged Japanese men and women. Br J Cancer, 2004. 90(1): p. 128-34.
18. Karppanen, H. and E. Mervaala, Sodium intake and hypertension. Prog Cardiovasc Dis, 2006. 49 (2): p. 59-75.
19. He, F.J., et al., Effect of salt intake on renal excretion of water in humans. Hypertension, 2001. 38(3): p. 317-20.
20. St-Onge, M.P., K.L. Keller, and S.B. Heymsfield, Changes in childhood food consumption patterns: a cause for concern in light of increasing body weights. Am J Clin Nutr, 2003. 78(6): p. 1068-1073.
21. Wigertz, K., et al., Racial differences in calcium retention in response to dietary salt in adolescent girls. Am J Clin Nutr, 2005. 81(4): p. 845-50.