The objective of the present study was to estimate the intake of Na (salt) and K by using 24-hour urine collection and to examine their relationship with BP in Moroccan adults. It was carried out in the spring to avoid the effect of seasonal variations on the estimated intakes of Na and K. Indeed, dietary Na excreted in the urine is underestimated by losing more than the normal fraction (approximately 4 to 12.7 mmol / day) due to the hot climate  and BP is mainly affected by seasonal variations in winter and summer  .
Results of this study showed that mean 24-hUNa was above the upper limit of 2000 mg/day (≈5g/day of salt), and mean 24-hUK was below the recommended adequate intake of 3510 mg. Since nearly 90% of Na consumed is excreted via urine  , Na intake in this study may be estimated at 3100 mg/day (2794 mg/0.90=3104 mg). This greatly exceeds the upper limit of Na intake of 2000 mg/day recommended by the WHO. Few data on Na intake in Moroccan adults were published. A pilot study carried out on a convenience-based sample of 132 of Moroccan adults reported an estimate that is similar to ours (2960 mg in men and 2769 mg in women) . An Estimate of Na intake of 3620 mg was observed in a cohort of Moroccan women of childbearing age using two 24-hour dietary recalls . Although repeated measurements were collected from the same participant (to account for day-to-day intraindividual variation in Na intake), Na intake in that study was less reliable compared to that found in our study, knowing the well-established measurement errors of dietary surveys . Hence, our estimate using 24-hour urinary excretion, the currently recommended method for estimating Na intake, is a reliable assessment for Na intake in the Moroccan population. We have shown that the majority (69.3%) of adults consume more than 2000 mg/day of Na, highlighting the relevance of implementing the national strategy to reduce the salt intake of the Moroccan population by 10% by 2029 as a voluntary target adapted by the country to fight against NCDs .
Sodium intake in the Eastern Mediterranean Region, reported in two systematic reviews   was high. The mean Na intake in the current study was within the range reported in the first systematic study published by Al Jawaldeh and colleagues . In that study, the highest estimate of Na intake was observed amongst adult men and women from Jordan (4100 mg/day), men from Lebanon (4800 mg/day), and women from the Republic of Iran (3900 mg/day). In the second systematic study, Powles J and colleagues reported a sodium intake of 3920 to 4200 mg/day in the Middle East and North Africa region and 4200 mg/day in Morocco . This is a much higher Na intake compared to our findings, however, in the review by Powles et al, the approach used to estimate Na intake in the Moroccan population was unclear.
Mean 24-hUK was 1898 mg. Potassium excretion is subject to large fluctuations, with only a fraction of 77% of dietary K being excreted in urine . Accordingly, mean K intake in this study may be about 2460 mg/day (1898 mg / 0.77 = 2465 mg). Even with such correction, the estimated K intake is still far below 3510 mg/day; the adequate level of K intake recommended by the WHO. Besides, only 8.4% of adults were consuming the recommended 3510 mg/day of K. This corroborates the results of previous studies showing low commitment of individuals to K intake recommendations  . Indeed, in Mexican healthy adults, only 2.3% of participants met the recommendations for dietary K  and in a Moroccan cohort, only one participant had a K intake above the cut-off set by the WHO to reduce the risk of chronic disease .
The vast majority of adults (84.9%) in our study did not meet the recommended Na/K intake ratio ≤ 1. This imbalance in the intake of Na and K may be a reflection of dietary behavior and the current food consumption patterns in Morocco. In fact, a nutritional transition has been observed in the country over recent decades . It concerned on the one hand, a diet which is increasingly based on processed foods (rich in Na and poor in K), in particular in urban regions such as the region of Rabat-Salé-Kénitra  and on the other hand, a decrease in the consumption fruits and vegetables. The STEPwise Survey-Morocco-2017-2018 showed that 76.3% of Moroccan adults consume less than 5 portions per day . A WHO/ Food and Alimentation Organization report , recommended to consume this amount of fruits and vegetables as a minimum requirement to prevent major diseases such as cardiovascular diseases and certain types of cancers on the basis of the high density of K and other nutrients that more than 5 portions may contain. This suggest that simultaneously with Na reduction strategies, it will be relevant to take measures to promote K intake at the population level; by increasing the individual's awareness of the importance of consuming fruits and vegetables and by making these types of foods more affordable.
We did not find a significant relationship between urinary Na or K and BP, even after adjustment for potential confounders. This result is consistent with findings from several other cross-sectional studies that also suggested an absence of a significant relationship between Na and K excretion with BP [43–45] . In contrast, others suggested a direct association of BP with Na and K intake [46–48]  . These contradictions could be explained by the lower range of both estimated K and Na shown in our study. Urinary K excretion in our study was low (1898 mg, equivalent to 2465 mg per day of K intake using the generally adopted conversion factor of 1.3) and ranged between 1000 and 3000 mg/day. This range showed no association with SBP in a recent study based on data from the Dietary Approaches to Stop Hypertension–Sodium trial . Similarly, Filippini and colleagues  performed a meta-analysis based on 32 studies and found a U‐shaped relationship between 24-hUK excretion and BP levels, with the presence of an association at low and high level but not at the intermediate level of K intake.
Additionally, our population was consuming a relatively low Na level. The K effect on lowering BP is shown to be more pronounced in subjects with high levels of Na intake . The Prospective Urban Rural Epidemiology (PURE) Study  and two studies conducted in the Chinese  and American  population have all shown a direct relationship between high BP and a diet high in Na. Comparing our study with the latter shows that there are differences both in the levels of Na excretion and in the methods used. However, we believe that the excretion level factor would be determining and could largely explain the difference in the relationship between Na excretion and K-arterial pressure. The Na estimate in the aforementioned studies was much higher than in our study (US population: 3650 mg/day, Chinese population: 3838 mg/day, multinational population (PURE study): 4930 mg/day our population: 2794 mg/day). The detailed analysis of the results of the PURE study shows that the slope of the association of Na excretion / BP depended on the levels of excretion. Transposing the excretion levels of 64% of the participants in our study, who had Na excretion below 3000 mg/day, to similar levels in the PURE study, showed the same result: an absence of a significant relationship. Levels of excretion in about a third (31% of the participants in our study with Na excretion between 3000 and 5000 mg/day) corresponded to levels in the PURE study for which a modest association was observed. What further strengthens our hypothesis is the fact that only 5% of our participants had a Na excretion greater than 5000 mg/day, levels for which in the PURE study, there was a stronger slope of association between BP and Na excretion. Methodologically, the Na intake in ,  was estimated using two consecutive urine samples over 24 hours from each individual, whereas in our case only one sample was taken. We performed a comparison in preliminary experiments with a small sample size and found that the small difference in the measurements was not significantly large. This gives the methodological difference less influence than the Na excretion level factor.
The lack of dependence of the estimated Na intake on the BMI is in contradiction with those of some previous studies  . The positive association between Na (salt) intake and BMI has generally been observed in developed countries. However, our results are similar to those of a study which showed no association between 24-hUNa and BMI . In addition, a recent cross-sectional study carried out in a cohort of Moroccan women of childbearing age living in the urban areas of the region of Rabat-Salé-Kénitra showed no association between energy intake (assessed using a validated 24-hour multipass dietary recall approach based on the most recent Moroccan food composition table) and BMI . These inconsistencies could be due, on the one hand, to the limit of BMI when used as a tool to assess energy intake or body size among different populations   or/and on the other due to differences in basic diet and salt sensitivity in Moroccan adults as well as their clinical characteristics compared to other populations. Salt-sensitive subjects have higher weight compared to salt-resistant subjects  . However, the examination of sensitivity to salt in our subjects, which could provide an explanation argument, was not realized.
This study has several limitations. Firstly, 24-h urine collection is still for now the recommended method to estimate Na intake . However, a single 24-h urine collection does not count for the intrapersonal variation in Na excretion. According to some authors, multiple 24-h urine collections are necessary to accurately assess habitual Na intake  . However, this approach is more cumbersome for participants knowing the highly documented difficulty for participants to collect a complete and valid 24-h urine collection [60–62]. This study primarily aims to estimate the mean Na intake of population. If provided by an appropriate number of individuals, a single 24-h urine collection would compensate the intrapersonal day-to-day Na excretion variation and safely estimate the mean population intake. Secondly, we collected the 24-hour urine samples during week-end in order to facilitate participation, however, 42% of adults refused to participate in the study or to collect the 24h urine sample (probably due to its cultural/psychological burden; people could find it embarrassing to bring the jar to their work place and keep collecting urine all 24-hour period). We did not examine the impact of differences in basic characteristics between the final sample and the firstly recruited population on Na and K intake level, but the final sample remain adequate for estimating Na and K intake in a group of subjects  . Finally, the sample size was sufficient for an accurate estimate of the mean Na and K intake, but was modest for examining the association between Na or K and BP.
Besides the aforementioned limits, this study used the 24-h urine collection known as the most accurate method to estimate Na intake, with the adoption of a rigorous protocol to minimize the risk of under-collection and overcollection and exclusion of invalid 24-h urine samples based on doubtful urinary volume, inacceptable collection period and the loss of more than one void. Our findings will help to enrich and fill the existing gaps in the national database with accurate information, which can help to implement the national strategy to reduce salt intake and promote the high priority of potassium intake in health programs.