Salt is an important ingredient of food. It is used in cooking food, as added salt, as preservative and in processed foods. However, increased consumption of salt is associated with increased risk of hypertension and cardiovascular events. The WHO Consultation of Experts held in Paris in 2006 and Luxembourg in 2007 recommended that daily per capita salt consumption be limited to 5 grams. [i] , [ii] At the same time, consumption of adequately iodized salt is considered as cornerstone in the control of iodine deficiency disorders. In 1994, a special session of the WHO and UNICEF Joint Committee on Health Policy recommended Universal Salt Iodization as a safe, cost-effective, and sustainable strategy to ensure sufficient intake of iodine by all individuals. [iii] The recommendations regarding salt consumption with respect to cardiovascular diseases and iodine deficiency disorders appear conflicting and may cause confusion among the stakeholders.
The salt intake varies across different socio-economic strata and geographical areas depending on culinary practices of the population. Mean sodium intake around the world was >100 mmol/day, and for many countries including those in Asia, mean intakes was >200 mmol/day. [iv] Processed foods are important source of salt and there is an increasing trend in consumption of processed foods in developing countries. [v] The INTERSALT study done in the year 1985-87 at 52 centres from 32 countries found the urinary sodium excretion, a proxy marker for sodium intake, to be very high in India. [vi] A task force of Indian Council of Medical Research (ICMR) constituted in 1996 reported the daily per capita consumption of salt to be 13.8 grams. [vii] A study in Chennai conducted in the year 2003 estimated the daily per capita salt consumption to be 8.5 grams. [viii] However, there is no nationally representative reliable data on salt consumption in India in recent times.
Salt consumption and risk of hypertension and cardiovascular diseases
Non-communicable diseases are responsible for 63% of global mortality, 48% of which is caused by cardiovascular diseases. Hypertension, one of the major risk factors for cardiovascular diseases, is estimated to cause 12.8% of global deaths. Mortality due to non-communicable diseases is likely to increase by 15% between 2010 and 2020. [ix] In India, 42% of all mortality is because of non-communicable diseases. [x] In India, a third of adult population is estimated to be suffering from hypertension. [xi]
Various studies have linked excess salt consumption to hypertension and cardiovascular diseases. In the Trials of Hypertension Prevention (TOPH) studies the risk of a cardiovascular event was 25-35 per cent lower in participants who adhered to sodium restriction when compared to the control group. [xii] Association between higher salt intake and mortality from cardiovascular diseases was also established in the Multiple Risk Factor Intervention Trial (MRFIT). [xiii] Association between high salt intake and blood pressure was further established in the Dietary Approaches to Stop Hypertension (DASH) study [xiv] . A meta-analysis of 105 randomized trials also found that salt restriction leads to a reduction in systolic blood pressure of 3.6 mm Hg. [xv] Another meta-analysis could find the significant reduction in blood pressure associated with salt restriction only in older hypertensive individuals while no significant result could be obtained in normotensive individuals. [xvi] The INTERSALT study also found a positive association between urinary sodium excretion and blood pressure, though the study was cross-sectional in nature. Studies in India also found a positive association between salt restriction to 5 grams/day and reduction in blood pressure., [xvii]
However, the evidence regarding association between excess salt consumption and hypertension and cardiovascular diseases are conflicting. A systematic review of studies found that most of the studies which reported a positive association between salt intake and hypertension were short-term intervention trials. [xviii] Similarly a meta-analysis of eight randomized trials, which had a follow up of more than 6 months, and assessed the effect of salt restriction on hypertension, could not found significant reduction in blood pressure among both hypertensive and normotensive individuals. [xix] A cohort study in Brazil also failed to find association between salt intake and hypertension, though only reported compliance with salt restriction was asked in this study. [xx] Similarly, another trial also could not find any significant reduction in blood pressure due to salt restriction. [xxi]
After reviewing the available evidence, the WHO Consultation of Experts recommended that daily per capita salt consumption be limited to 5 grams., However, a recent meta-analysis of randomized trials where the follow period was more than 6 months, though found an association between salt restriction and reduction in blood pressure, could not find any reduction in cardiovascular mortality. [xxii]
Salt consumption and Control of Iodine Deficiency Disorder
Iodine Deficiency Disorders (IDD) constitutes the single largest cause of preventable brain damage worldwide. [xxiii] IDD comprise of a spectrum of diseases including goitre, cretinism, hypothyroidism, brain damage, abortion, still birth, mental retardation, psychomotor defects and hearing and speech impairment. It was reported that Iodine Deficiency causes a reduction of 13.5 IQ points in children and may lead to major learning disabilities. [xxiv] Globally two billion people are at risk of iodine deficiency disorders due to insufficient iodine intake. [xxv] In India, Iodine Deficiency Disorder is endemic, defined as prevalence of more than 10%, in 303 districts out of 365 districts surveyed. [xxvi] . An estimated 350 million people are at risk of IDD in India. Majority of consequences of IDD are invisible and irreversible but at the same time they are totally preventable.
Iodine deficiency disorders (IDD) are disease of the soil. Due to various geological events, the iodine content of soil and consequently of plant food products remain poor. Hence, iodine supplementation is essential to prevent iodine deficiency disorders. Salt is considered the ideal vehicle for iodine supplementation. It is consumed universally, does not alter the taste or appearance of the salt, iodization of salt is simple, easy and cost-effective process, and the iodization process is easy to monitor. There is a strong and consistent global and national evidence of the impact of universal salt iodization strategy to prevent and control IDD. Effectiveness of salt iodization to control Iodine Deficiency Disorder in India was established in a landmark study in the Kangra valley in Himachal Pradesh from 1956 to 1972. [xxvii] Globally iodine level in salt ranges from 20 to 40 Parts per Million (PPM) based on an assumption of average consumption of 5 to 10 grams of salt. [xxviii] The recommended salt iodine fortification of 30 PPM at production and 15 PPM at consumption level in India provides 150 µg of iodine per day assuming daily salt consumption of 10 gm.
The Way Forward
There is not enough information on the quantity of salt intake and the form in which it is taken in India. Information on dietary sources of sodium and sodium consumption in the population groups should be collected through appropriate surveillance systems (E.g. STEPS or national nutrition surveys) to formulate appropriate policy in this regard. There is also need to collect more information regarding the iodine content in various commonly consumed food items in various cultural and geographic settings in India.
The consumption of processed food is increasing and becoming the major mode of consumption of salt. There is a need to formulate the policies that any salt meant for the human consumption either directly or indirectly must have iodized salt in appropriate quantity. It was found that the processed food industry is in a favour of legislative framework for use of iodized salt in processed foods. Modification in existing regulations like Food Safety and Standards (Food Products Standards and Food Additives) Regulations, 2011 to this effect will help in achieving the delivery of adequate quantity of iodine through salt. The packaged and processed food industry should be engaged and encouraged to reformulate, appropriately label, and make available products with reduced salt and to make use of iodized salt in all their products.
There is also a need to have a relook at the level of iodine fortification in the salt. It should depend upon the type of food consumed and their salt and iodine content, and the iodine nutritional requirements of various population sub-groups. Salt restriction strategies should be tailored according to the needs and vulnerability of different groups. Another factor which is important in Indian context is the stability of iodine in salt. In India, salt is required to have 30 PPM at the production level. If the stability of iodine can be increased with better packaging and storage practices, more iodine can be delivered at the lower level of salt intake. However, there is no robust data on the stability of iodine in iodized salt and more evidence needs to be generated in this regard.
In view of the implications of morbidity and mortality associated with cardiovascular diseases and the effect of iodine deficiency disorders, it is imperative that the efforts to control both should be synchronized. The apparently conflicting recommendations in regard to salt intake in case of both disorders may confuse policy makers, food industry and general public. It is important to convey the message that salt reduction strategy and universal salt iodization strategy is compatible and harmonious.
