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Impacts of a national strategy to reduce population salt intake in England: serial cross sectional study.
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PMID:  22238665     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
BACKGROUND: The UK introduced an ambitious national strategy to reduce population levels of salt intake in 2003. The aim of this study was to evaluate the impact of this strategy on salt intake in England, including potential effects on health inequalities.
METHODS: Secondary analysis of data from the Health Survey for England. Our main outcome measure was trends in estimated daily salt intake from 2003-2007, as measured by spot urine. Secondary outcome measures were knowledge of government guidance and voluntary use of salt in food preparation over this time period.
RESULTS: There were significant reductions in salt intake between 2003 and 2007 (-0.175 grams per day per year, p<0.001). Intake decreased uniformly across all other groups but remained significantly higher in younger persons, men, ethnic minorities and lower social class groups and those without hypertension in 2007. Awareness of government guidance on salt use was lowest in those groups with the highest intake (semi-skilled manual v professional; 64.9% v 71.0% AOR 0.76 95% CI 0.58-0.99). Self reported use of salt added at the table reduced significantly during the study period (56.5% to 40.2% p<0.001). Respondents from ethnic minority groups remained significantly more likely to add salt during cooking (white 42.8%, black 74.1%, south Asian 88.3%) and those from lower social class groups (unskilled manual 46.6%, professional 35.2%) were more likely to add salt at the table.
CONCLUSIONS: The introduction a national salt reduction strategy was associated with uniform but modest reductions in salt intake in England, although it is not clear precisely which aspects of the strategy contributed to this. Knowledge of government guidance was lower and voluntary salt use and total salt intake was higher among occupational and ethnic groups at greatest risk of cardiovascular disease.
Authors:
Christopher Millett; Anthony A Laverty; Neophytos Stylianou; Kirsten Bibbins-Domingo; Utz J Pape
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Publication Detail:
Type:  Evaluation Studies; Journal Article; Research Support, Non-U.S. Gov't     Date:  2012-01-04
Journal Detail:
Title:  PloS one     Volume:  7     ISSN:  1932-6203     ISO Abbreviation:  PLoS ONE     Publication Date:  2012  
Date Detail:
Created Date:  2012-01-12     Completed Date:  2012-05-14     Revised Date:  2013-06-26    
Medline Journal Info:
Nlm Unique ID:  101285081     Medline TA:  PLoS One     Country:  United States    
Other Details:
Languages:  eng     Pagination:  e29836     Citation Subset:  IM    
Affiliation:
Department of Primary Care and Public Health, Imperial College London, London, United Kingdom.
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MeSH Terms
Descriptor/Qualifier:
Adolescent
Adult
Aged
Aged, 80 and over
Awareness
Cohort Studies
Cross-Sectional Studies
Down-Regulation
Eating / physiology*
England / epidemiology
Female
Health Planning Guidelines
Humans
Hypertension / epidemiology,  prevention & control
Male
Middle Aged
National Health Programs*
Population
Program Evaluation
Sodium Chloride, Dietary / administration & dosage*
Young Adult
Chemical
Reg. No./Substance:
0/Sodium Chloride, Dietary
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Journal ID (nlm-ta): PLoS One
Journal ID (publisher-id): plos
Journal ID (pmc): plosone
ISSN: 1932-6203
Publisher: Public Library of Science, San Francisco, USA
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Millett et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Received Day: 10 Month: 6 Year: 2011
Accepted Day: 6 Month: 12 Year: 2011
collection publication date: Year: 2012
Electronic publication date: Day: 4 Month: 1 Year: 2012
Volume: 7 Issue: 1
E-location ID: e29836
ID: 3251604
PubMed Id: 22238665
Publisher Id: PONE-D-11-10598
DOI: 10.1371/journal.pone.0029836

Impacts of a National Strategy to Reduce Population Salt Intake in England: Serial Cross Sectional Study Alternate Title:Population Salt Intake in England 2003–2007
Christopher Millett1
Anthony A. Laverty1*
Neophytos Stylianou1
Kirsten Bibbins-Domingo2
Utz J. Pape1
Murielle Bochudedit1 Role: Editor
1Department of Primary Care and Public Health, Imperial College London, London, United Kingdom
2Departments of Medicine, Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, United States of America
University Institute of Social and Preventive Medicine, Switzerland
Correspondence: * E-mail: a.laverty@imperial.ac.uk
Contributed by footnote: Conceived and designed the experiments: CM. Performed the experiments: AL NS. Analyzed the data: AL NS UP. Contributed reagents/materials/analysis tools: AL NS UP. Wrote the paper: CM AL KBD.

Introduction

Strategies to reduce population levels of salt intake may represent a promising and highly cost effective way of reducing the growing burden of non-communicable disease, particularly in resource constrained settings. Estimates suggest that achieving a 15% reduction in population level salt intake would avert 8.5 million deaths in low and middle income countries over ten years at an annual cost of between 4 to 32 US cents per person. [1] Recent modelling studies projected that reductions in mean daily salt intake in North America and Europe would result in large reductions in cardiovascular disease and considerable cost savings to health care systems. [2], [3], [4], [5] For example, a 3 g/day reduction in salt intake in the US population would decrease the annual number of new cases of CHD by up to 120,000, stroke by 66,000 and myocardial infarction by 99,000 and decrease the annual number of deaths from any cause by up to 92,000. [2]

Accumulating evidence about beneficial impacts of salt reduction on population health has led the World Health Organization to set a global target for adult salt intake (5 g/day) and recommend that national governments institute strategies to achieve this. [6] One of the most ambitious attempts to reduce population salt intake has been undertaken in the UK. [7] This national strategy introduced in 2003 involves voluntary agreements with the food industry to reduce salt content in processed foods, improving food labeling and public awareness campaigns to change personal behavior i.e. reduce salt added during cooking. [8] Recent evidence supports the UK approach of working with industry to reduce salt in processed food over other strategies, such as a salt tax. [3] The UK strategy was strengthened in 2006 when a national target was set to reduce population salt intake to 6 grams by 2010 (this target has now been delayed until 2012) reflecting guidance issued by the UK's Committee on Medical Aspects of Food and Nutrition Policy in 1994 and reiterated by the Scientific Advisory Committee on Nutrition in 2003. [9], [10]

Whole population approaches to prevention may be more likely to reduce social inequalities in health outcomes than interventions targeting high risk groups, although this has been contested. [11], [12] The UK salt reduction strategy might be expected to reduce known inequalities in cardiovascular disease (CVD) for several reasons. First, consumption of fresh fruit and vegetables is lower [13] and consumption of processed foods (which contain approximately 75–80% of dietary salt [14]) may be higher in poorer communities who are likely to benefit most from comprehensive reductions in salt content in food by industry. Second, the strategy involves making greater reductions in salt in cheaper food products which are disproportionately consumed by poorer households. [7] Third, the public awareness campaign component of the strategy was targeted at women from lower social class groups, as these women are regarded as the “gatekeepers” for food purchase and preparation in many UK households. [15] Finally, uniform reductions in salt intake appear to produce greater decreases in blood pressure in older patients and in ethnic minorities who are at higher risk of CVD. [16], [17] The aim of this study was to assess the impact of the strategy on population salt intake, including potential impacts on inequalities, using national survey data from the Health Survey for England.


Methods
Sampling and data collection

The data used in this study were derived from the Health Survey for England (HSE). The HSE is an annual survey of people living in private households and is a primary mechanism for monitoring population health in England. The methods of the survey are described in detail elsewhere. [18] Briefly, a two-stage stratified sampling process is employed to obtain an independent, nationally representative sample each year. The core sample from the general population is boosted by sampling from population groups of interest in some years i.e. persons from ethnic minorities in 2004. Interviewers obtain household, socioeconomic and personal details, information on health and illness, and health service use from respondents. Respondents aged above the age of 16 years are then visited separately by a trained nurse. The nurse visit involves anthropometric measurements, blood and urine samples. Respondents are asked for information about prescribed medications.

The percentage of adult respondents (≥16 years) to the HSE who provided a urine sample in each year of the study (2003–2007) was 9.0%, 28.1%, 34.9%, 41.3% and 29.7%.

Variables

Our main outcome measure was daily salt intake and our secondary outcome measures were knowledge of national guidance on salt intake and self reported information on whether salt is added during cooking or at the dinner table. Knowledge of guidance and use of salt results are presented in Tables 1 and 2. Participants were asked “What do you think are the guidelines for maximum daily salt intake?”, and those correctly identifying 6 grams per day were classified as being aware of the target.

Daily salt intake was estimated from a voluntary spot urine test, where urine was collected mid flow in a 100 ml beaker. 10 ml of this urine was then collected in a special collection syringe by the participant, and this 10 ml sample was used for analysis. All samples were processed by the same analyser brand (Olympus AU 640) in different laboratories and all of them underwent internal as well as external quality control and assessment, details of which can be found in the relevant reports. [19] Sodium values in the HSE dataset was transformed into a measure of daily salt intake using the accepted conversion method of 1 gram of salt equalling 17.1 mmol of sodium. [14] Our predictor variables were age, gender, ethnicity, social class and hypertension status. We generated a categorical variable for age; 16–34, 35–54, 55–74 and 75+ years. We categorised ethnicity into white, black and south Asian groups. We used the UK Registrar General's classification of social class as a measure of socio-economic status but due to small numbers we collapsed this into two groups (non-manual, manual) for our analysis of salt intake. Hypertension was defined as having a systolic blood pressure >140 mm Hg or a diastolic blood pressure of >90 mm Hg or taking antihypertensive medications.

Statistical analysis

We present non-weighted findings as they did not differ markedly to findings weighted to weights produced by the Health Survey for England, designed to correct for selection of households, non response, and population profile. [20] Since the distribution of salt intake was positively skewed, the data was logarithmically transformed before linear regression. Geometric means and their 95% confidence intervals are presented in Table 3. We employ a time-series regression model to estimate the trend of salt intake between 2003 and 2007 with one coefficient for the time-effect. Results from these regressions are presented in Table 4 transformed back into their original scale to allow more meaningful interpretation.

For the regression baseline effects were included for the factors age, gender, social class, ethnicity and hypertension. To disentangle time-dependent effects of the factors, we built additional models for each factor containing all baseline effects, the time-dependent interaction effect with the selected factor. Each model also included a separate term for each ethnic group to take account of the varying trends and group composition over time.

We abstain from a full model including all time-dependent interactions as this model would be complex with many parameters. Thus, the models presented in Table 4 are of the trends for the results presented by each dependent variable but controlling for other variables as baseline effects. All statistical analysis was performed using Stata 10.


Results
1. Knowledge of national guidance on daily salt intake in 2007

Seven in ten (68.8%) respondents were aware that the government had issued guidance advising that they should restrict their salt intake (Table 1). Awareness was lower in the youngest aged group (16–34 years) than the older age groups. Women were significantly more likely to be aware of the guidance than men (73.0% v 63.4%; AOR 1.57 95% CI 1.41, 1.74) Black and south Asian respondents were significantly less likely to be aware of the guidance than white respondents (black 53.6% v south Asian 40.8% v white71.1%). Respondents from manual social class groups were significantly less likely to be aware than non-manual groups. One third of respondents (33.3%) were able to state that the recommended daily level of salt intake was 6 grams. Women were more likely to be aware of this recommendation than men and black respondents were more likely to be aware of this recommendation than white respondents (56.3% vs. 32.9%; AOR 2.62 95% CI 1.29, 5.31).

2. Voluntary salt use in cooking and at the table

The percentage of respondents who reported adding salt during cooking decreased significantly from 52.0% in 2003 to 45.8% in 2007 (p<0.001 – Table 2). Older respondents (≥55 years), men, respondents from ethnic minority groups and those with hypertension were significantly more likely to add salt during cooking in 2003 and 2007 (Table 2). There was no difference in the percentage reporting adding salt during cooking by social class grouping in either year.

The percentage of respondents who reported adding salt to food at the table decreased significantly from 56.5% in 2003 to 40.2% in 2007 (p<0.001). Men and respondents from lower social class groups were significantly more likely to add salt at the table than women and those from higher social class groups respectively in 2003 and 2007. Respondents from ethnic minority groups and those with hypertension were significantly less likely to add salt at the table than the white group and those without hypertension respectively in both years.

3. Trends in daily salt intake from excretion data, 2003–2007

Mean salt intake decreased significantly across all groups between 2003 and 2007 (Tables 3 and Table 4). Findings from our linear time-series regression models suggest that these reductions were uniform between age, sex, social class and ethnic groups and by hypertension status (Table 4). For example, salt intake in white respondents as the reference group declined significantly (0.173 grams/day p<0.001) every year between 2003 and 2007 and declines in black respondents were not found to be significantly different 0.394 grams/day, p value for difference = 0.465), and the same was true of South Asians. Similarly, there is no significant difference in reductions in salt intake between manual and non-manual workers (p value for difference = 0.272). These results are robust against using a more differentiated set of social class. Consequentially, initial differences in salt intake between groups evident in 2003, i.e. higher intake in younger people, men, ethnic minorities and lower social class groups and respondents without hypertension, persisted in 2007 (Table 3).


Discussion
Main findings

Our findings suggest that the UK's salt reduction strategy has resulted in significant but modest reductions in population level salt intake. These reductions were broadly uniform across groups which meant that intake remained higher in younger people, men, ethnic minorities and lower social class groups. Voluntary use of salt during food preparation reduced significantly during the study period. Respondents from ethnic minority groups remained much more likely to add salt during cooking and those from lower social class groups remained more likely to add salt at the table. The higher intakes in these groups continued despite being targeted within the campaign and means that they remain at elevated risk of cardiovascular diseases.

Our findings that salt intake is decreasing by 0.175 grams/day per year are consistent with the limited data available from 24 hour urine surveys conducted in the UK to monitor this strategy which found that salt intake decreased by 0.2 grams/day per year (from 9.0 to 8.6 grams) between 2006 and 2008. [21] The higher salt intake in men identified in our study may not only reflect greater energy consumption but lower knowledge of government guidance and greater voluntary use of salt in food preparation. Consistent with previous research we found higher salt intake in young people and ethnic minorities and increased voluntary salt use in lower socio-economic groups. [21], [22], [23]

Precise data on the reductions of salt across the whole diet is difficult to assemble, but the Federation of Bakers claim that UK bakers have reduced the amount of salt in bread by 10% in the last three years, [24] while the Association of Cereal Food Manufacturers in 2007 claimed to have reduced salt levels by 38% from 1998 levels. [25] A review commissioned by the Food Standards Agency found that there were reductions of up to 70% were found in some foods, and highlighted large improvements in areas where different manufacturers worked together under trade or umbrella organisations. [26] The National Diet and Nutrition Survey remains an important part of policy for measuring nutritional status in the UK population, and is due to report on salt intake in 2012. [27]

Strengths and limitations

Our study had a number of strengths and limitations. The HSE is a representative national survey and a primary mechanism for monitoring population health in England. Only one in three respondents provided a urine sample in most years of the study period. However, the characteristics of respondents who provided a sample did not differ from those that did not in terms age, sex, ethnicity or social class. Comparing outcomes across time using cross-sectional surveys may introduce bias, given that there may be systematic differences in respondents sampled in the different survey years. Estimates of salt intake were derived from spot rather than the “gold standard” 24 hour urine samples. Spot urines are not suited to measuring intake in individuals but available information suggests that this method is appropriate for population monitoring as measurement bias as they are, is likely to be consistent over time and between groups and are biased toward underestimating salt intake. [23], [28] Data from comparisons of spot and 24 hour urine sampling report the non-parametric correlation Spearman coefficients between these two methods to be between 0.42 and 0.50 for sodium, and note that spot urine tests follow the same patterns as 24 hour sampling. Taken together, the authors suggest that spot urine tests can be used to differentiate between groups in the population in a similar way to 24 hour samples. [28]

As the decision to provide a urine sample was voluntary there may be some degree in self selection. The proportion of the overall population providing a sample in each year ranged from 9.0% to 41.3% which may have affected the results presented here. However, analyses using the weights provided by the Health Survey for England to correct for these issues did not influence the results found.

The modest reductions in population level salt intake identified in our study coincided with improvements in blood pressure levels. Data from the Health Survey for England have shown steady improvements in controlling blood pressure from 1994 [29] with particularly large improvements between 2003 and 2006. However, we were unable to isolate the impacts of the salt reduction strategy from other primary and secondary prevention interventions, including the provision of financial incentives to general practitioners, to improvements in blood pressure control over the study period [19], [30], [31].

The data used for this study are now four years old and our findings may not reflect current public knowledge about recommended levels of salt intake or patterns in intake. As the data is limited to 2003 after the intervention, we cannot measure the trend of salt intake prior to the reduction. Therefore, reduced salt intake could be due to a previous trend or a parallel intervention. Based on other evidence however, salt intake was constant before the intervention [23]. We were also unable to measure awareness of salt guidelines prior to 2007, as this year was the first year for which this data was collected.

Implications for policy

Implementation of a national salt reduction strategy in the UK has been associated with modest reductions in population levels of salt intake [32]. The Food Standards Agency reported that as of 2009 there were over 90 organisations committed to reducing salt in their products ranging from manufacturers, retailers, trade associations and the catering sector [15]. This wide range of support is commendable however, ongoing support for the strategy by the UK government will be essential to achieve the target of an average daily salt intake of 6 grams by 2012. Despite a government commitment in the recently published public health white paper to work with industry to achieve “further reformulation of food to reduce salt” [33] it is of concern that responsibility for nutrition policy was removed from the independent Food Standards Agency in October 2010 [34]. Mandatory targets for industry to reduce salt in processed foods and mandatory food labelling should be considered if more rapid progress toward the 6 grams per day target is not achieved. Evaluation of the Finnish salt reduction strategy, which was implemented in 1979 and had voluntary agreements with the food industry, suggest that average daily salt intake decreased by only 3 grams per day over a 20 year period (from 12 grams per day in 1979 to 9 grams per day in 2002) [35]. Our finding that the public awareness campaign resulted in only small reductions in voluntary use of salt in food preparation further highlight the importance of working with to industry to achieve large reductions in the salt content of processed foods. While we were unable to determine the relative contribution of the Food Standards Agency's public awareness campaign and reformulation of processed foods by industry to the reductions in salt intake identified, we would agree with calls for comprehensive salt reduction policies with a multi-pronged approach. Sodium reduction strategies need to be tailored to individual country contexts, including sources of salt within the diet, but may include communication strategies with the public; household level interventions, reformulation of foods; engagement with industry, possible regulation and ongoing monitoring of salt intake levels [36].

Policy makers in other countries should consider following the UK approach of designing and implementing salt reduction strategies in ways to bring disproportionate benefit to disadvantaged communities who experience higher rates of cardiovascular disease. Our findings suggest that persons from manual occupational groups and ethnic minorities achieved similar reductions in salt intake as non-manual and white ethnic groups. It is important that monitoring strategies for salt reduction strategies currently being developed by the World Health Organisation consider equity impacts explicitly in their evaluation frameworks [37].


Notes

Competing Interests: The authors have declared that no competing interests exist.

Funding: CM is funded by the Higher Education Funding Council for England and the National Institute for Health Research. AL is funded by the National Institute for Health Research. The Department of Primary Care and Public Health at Imperial College is grateful for support from the National Institute for Health Research Biomedical Research Centre Funding scheme, the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care scheme, and the Imperial Centre for Patient Safety and Service Quality. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Tables
[TableWrap ID: pone-0029836-t001] doi: 10.1371/journal.pone.0029836.t001.
Table 1  Awareness of salt guidelines (2007).
n % aware of guidance AOR (95% CI) % aware of 6 g/d target* AOR (95% CI)
Overall 6384 68.8 - 33.3 -
Age 16–34 1586 61.0 ref 35.6 ref
35–54 2263 69.2 1.43 (1.25, 1.64) 31.9 0.85 (0.66, 1.09)
55–74 1911 75.5 1.96 (1.70, 2.27) 32.8 0.93 (0.72, 1.20)
75+ 624 66.4 1.26 (1.04, 1.53) 28.1 0.71 (0.44, 1.15)
Sex Men 2831 63.4 ref 29.3 Ref
Women 3553 73.0 1.57 (1.41, 1.74) 36.3 1.37 (1.12, 1.68)
Ethnicity White 5780 71.1 ref 32.9 Ref
South Asian 316 40.8 0.28 (0.22, 0.36) 27.7 0.78 (0.45, 1.36)
Black 153 53.6 0.47 (0.34, 0.65) 56.3 2.62 (1.29, 5.31)
Social class I - professional 324 71.0 ref 34.6 Ref
II- managerial technical 1906 74.5 1.19 (0.92, 1.55) 34.3 0.99 (0.64, 1.52)
III - skilled non-manual 1435 71.8 1.04 (0.80, 1.36) 33.6 0.96 (0.61, 1.50)
III - skilled manual 996 61.9 0.66 (0.50, 0.87) 29.1 0.78 (0.48, 1.27)
IV - semi-skilled manual 1072 64.9 0.76 (0.58, 0.99) 32.1 0.90 (0.55, 1.45)
V - unskilled manual 296 66.2 0.80 (0.57, 1.12) 32.9 0.93 (0.49, 1.74)
Hypertension No 5524 68.0 ref 33.3 Ref
Yes 860 73.4 1.29 (1.10, 1.52) 33.2 1.00 (0.74, 1.33)

AOR: adjusted odds ratios.

*This based on participants being able to identify the guideline amount as 6 grams per day.


[TableWrap ID: pone-0029836-t002] doi: 10.1371/journal.pone.0029836.t002.
Table 2  Self reported voluntary use of salt during cooking and at table.
2003 2007
N Add salt in cooking Add salt at table N Add salt in cooking Add salt at table
% AOR (95% CI) % AOR (95% CI) % AOR (95% CI) % AOR (95% CI)
Overall 8621 52.0 56.5 6,281 45.8 40.2
Age 16–34 1865 48.0 ref 57.2 ref 1403 44.2 ref 37.4 ref
35–54 3186 47.3 0.97 (0.87, 1.09) 55.6 0.94 (0.83, 1.05) 2282 40.1 0.84 (0.74, 0.97) 40.7 1.15 (1.00, 1.32)
55–74 2732 56.3 1.40 (1.24. 1.57) 56.8 0.98 (0.87, 1.11) 1941 48.0 1.16 (1.01, 1.34) 41.4 1.18 (1.02, 1.36)
75+ 838 64.7 1.98 (1.68, 2.35) 57.0 0.99 (0.84, 1.17) 655 62.4 2.10 (1.74, 2.54) 41.1 1.17 (0.96, 1.41)
Sex Men 3896 53.4 ref 60.9 ref 2866 48.0 ref 43.2 ref
Women 4725 50.9 0.90 (0.83, 0.98) 52.9 0.72 (0.66, 0.78) 3415 43.9 0.85 (0.77, 0.94) 37.8 0.80 (0.72, 0.88)
Ethnicity White 8212 50.5 ref 56.9 ref 5828 42.8 ref 41.2 ref
South Asian 277 87.4 6.79 (4.75, 9.70) 50.9 0.79 (0.62, 0.78) 291 88.3 10.08 (7.02, 14.47) 28.5 0.57 (0.44, 0.74)
Black 132 72.7 2.62 (1.78, 3.85) 43.2 0.58 (0.41, 0.82) 162 74.1 3.81 (2.67, 5.44) 24.7 0.47 (0.33, 0.67)
Social class I - professional 452 52.7 ref 51.6 ref 327 45.9 ref 35.2 ref
II- managerial technical 2597 49.3 0.87 (0.71, 1.07) 55.7 1.18 (0.97, 1.44) 1964 42.7 0.88 (0.69, 1.11) 37.7 1.12 (0.87, 1.43)
III - skilled non-manual 2099 51.7 0.96 (0.79, 1.18) 53.3 1.07 (0.88, 1.32) 1478 45.2 0.97 (0.77, 1.24) 38.0 1.13 (0.88, 1.45)
III - skilled manual 1586 54.4 1.07 (0.87, 1.32) 62.0 1.54 (1.24, 1.90) 1067 48.0 1.09 (0.85, 1.40) 45.2 1.52 (1.17, 1.96)
IV - semi-skilled manual 1441 53.7 1.04 (0.84, 1.29) 57.3 1.26 (1.02, 1.56) 1119 49.2 1.14 (0.89, 1.46) 42.5 1.36 (1.05, 1.76)
V - unskilled manual 446 54.5 1.08 (0.83, 1.40) 52.5 1.33 (1.02, 1.73) 326 47.9 1.08 (0.80, 1.47) 46.6 1.61 (1.18, 2.21)
Hypertension No 1808 51.3 ref 57.4 ref 5406 45.1 ref 41.4 ref
Yes 6813 54.7 1.15 (1.04, 1.40) 53.2 0.85 (0.76, 0.94) 875 50.1 1.22 (1.06, 1.47) 33.1 0.70 (0.60, 0.82)

AOR: adjusted odds ratios.


[TableWrap ID: pone-0029836-t003] doi: 10.1371/journal.pone.0029836.t003.
Table 3  Trends in geometric mean daily salt intake (grams/day)*.
Year
Variable Category 2003 2004 2005 2006 2007
n Mean 95% CI n Mean 95% CI n Mean 95% CI n Mean 95% CI n Mean 95% CI % change 2003–2007
Overall 1668 5.29 5.1–5.5 2840 5.99 5.9–6.1 4643 4.80 4.7–4.9 8844 4.73 4.7–4.8 4269 4.55 4.5–4.7 −14.0
Age 16–34 388 6.56 6.1–7.0 971 7.13 6.9–7.4 1059 6.19 5.9–6.4 1856 6.17 6.0–6.4 950 5.94 5.7–6.2 −9.5
35–54 650 5.26 5.0–5.5 1224 5.94 5.7–6.2 1736 5.05 4.9–5.2 3331 4.91 4.8–5.0 1571 4.77 4.6–4.9 −9.3
55–74 499 4.72 4.5–5.0 551 4.79 4.5–5.1 1445 3.96 3.8–4.1 2844 4.00 3.9–4.1 1357 3.84 3.7–4.0 −18.6
75+ 131 4.38 4.0–4.8 94 4.05 3.6–4.6 403 3.90 3.7–4.1 813 3.96 3.8–4.1 391 3.60 3.4–3.8 −17.8
Sex Men 735 6.10 5.9–6.4 1279 6.36 6.2–6.6 2085 5.50 5.4–5.7 3977 5.41 5.3–5.5 1926 5.16 5.0–5.3 −15.4
Women 933 4.73 4.5–4.9 1561 5.70 5.5–5.9 2558 4.26 4.1–4.4 4667 4.24 4.2–4.3 2343 4.12 4.0–4.2 −12.9
Ethnicity White 1573 5.21 5.0–5.4 638 4.81 4.6–5.1 4397 4.74 4.6–4.8 8215 4.63 4.6–4.7 3902 4.47 4.4–4.7 −14.2
South Asian 50 5.46 4.6–6.5 1245 6.14 5.9–6.4 121 6.15 5.5–6.9 320 6.44 6.0–6.9 186 5.58 5.1–6.1 +2.2
Black 26 8.44 7.0–10.1 650 6.89 6.6–7.2 45 6.30 5.1–7.7 168 6.52 5.9–7.2 90 5.52 4.8–6.4 −34.6
Social class Non Manual 944 5.04 4.8–5.3 1337 5.91 5.7–6.1 2783 4.52 4.4–4.6 5219 4.42 4.3–4.5 2510 4.32 4.2–4.4 −14.3
Manual 661 5.61 5.3–5.9 1066 6.02 5.8–6.3 1675 5.24 5.1–5.4 3260 5.15 5.0–5.3 1562 4.87 4.7–5.0 −13.2
Hypertension Yes 276 4.84 4.5–5.2 395 5.00 4.7–5.3 815 4.30 4.1–4.5 1595 4.21 4.1–4.3 3477 4.09 3.9–4.3 −15.5
No 1072 5.40 5.2–5.6 1903 6.30 6.1–6.4 2938 4.90 4.8–5.0 5957 4.83 4.8–4.9 792 4.67 4.6–4.8 −13.5

*Note that these values come from a spot urine test, and so do not reflect intake over whole 24 hour periods.


[TableWrap ID: pone-0029836-t004] doi: 10.1371/journal.pone.0029836.t004.
Table 4  Trends in salt intake from linear time-series regression models.
Model Category Adjusted geometric mean in 2003 (g/d) Regression coefficient for slope (relative to reference category) Overall regression coefficient for slope 95% Lower CI (Log scale) 95% Upper CI (Log scale) Reduction in grams/day per year P value for differences between groups*
Age 16–34 6.77 ref −0.036 −0.055 −0.018 −0.242 <0.001
35–54 5.24 0.009 −0.030 −0.013 0.031 −0.155 0.418
55–74 4.74 −0.003 −0.040 −0.026 0.020 −0.186 0.788
75+ 4.36 0.002 −0.040 −0.032 0.036 −0.171 0.903
Sex Men 6.05 ref −0.038 −0.050 −0.018 −0.226 <0.001
Women 4.66 0.009 −0.030 −0.007 0.025 −0.138 0.265
Ethnicity White 5.21 ref −0.034 −0.043 −0.025 −0.173 <0.001
South Asian 5.14 0.016 −0.010 −0.016 0.047 −0.051 0.333
Black 8.09 −0.016 −0.050 −0.057 0.026 −0.394 0.465
Social Class Non Manual 5.01 ref −0.040 −0.048 −0.026 −0.197 <0.001
Manual 5.60 0.009 −0.030 −0.030 0.010 −0.165 0.272
Hypertension Normotensive 5.38 ref −0.040 −0.046 −0.027 −0.211 <0.001
Hypertensive 4.78 0.014 −0.030 −0.007 0.034 −0.141 0.186
Year overall 5.25 −0.034 −0.034 −0.043 −0.025 −0.175 <0.001

*p values for reference categories reflect differences of the trend from zero, while all other values reflect differences from the reference group trend.



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