Similar to the sodium AI, the sodium UL is based on moderate physical activity (nonstrenuous physical activity) and based on usual energy intakes as cited for each age group under “Findings by Life Stage and Gender Group.”

Much of the data used to set the UL were derived from trials that included both young and middle-aged adults. Hence this UL applies to men and women ages 19 to 50 years. Since chloride is assumed to be in foods in equimolar amounts, the UL for chloride is set at an equimolar basis, 3.6 g (100 mmol)/day.

In observational studies, the rise in blood pressure in response to higher sodium intake increases with age (Law et al., 1991a). In trials, middle- and older-age persons (> 45 years) have greater sensitivity to changes in sodium intake than younger adults (Vollmer et al., 2001). As documented previously, elderly persons are especially sensitive to changes in sodium intake (Johnson et al., 2001). Common problems in aging are excessive retention of sodium and volume overload. In elderly, the capacity to excrete sodium, as well as the diurnal variation in its excretion, are altered. Both the decrease in glomerular filtration rate and reduced responsiveness of the renin-angiotensin-aldosterone system seen with aging are major factors that limit the ability of the kidney to excrete an acute sodium load. Other factors, such as dopamine, prostaglandins, intrarenal hemodynamics, activity of the α-adrenergic system within the kidney, and renal nerve activity, may also play a role.

Because of increased salt sensitivity in the elderly and due to the higher risk of blood pressure-related cardiovascular disease, the UL