"These results are important as they explain in part why people of low socio-economic background are more likely to develop high blood pressure (hypertension) and to suffer disproportionately from strokes, heart attacks and renal failure," commented study author Francesco Cappuccio (University of Warwick, UK) in a press statement.
Cappuccio and team surveyed 2105 White men and women aged 19-64 years who participated in the British National Diet and Nutrition Survey during 2000-2001. Salt intake was measured via 7-day dietary records and 24-hour urinary sodium measurements.
As reported in BMJ Open, the investigators found that the median dietary sodium intake was 2611 mg/day, which corresponds to an approximate salt intake of 6.5 g/day. This may have been an underestimate, however, as the median 24-hour urinary sodium excretion was 140.6 mmol/day or an estimated 8.2 g/day of salt. The researchers report that people living in Scotland had significantly higher sodium intakes than those living in England and Wales.
Based on 7-day dietary record data, people with the lowest educational achievement (no qualifications) consumed approximately 5% more dietary sodium than those with A-level education or above, following adjustment for geographic location.
Similarly, based on 24-hour urinary sodium measures and accounting for geographic location, participants with no educational attainment and from households with the lowest social class (household main wage earner in manual work) consumed 4% and 9% more salt than those with A-levels or equivalent qualifications or those from households with the highest social class (household main wage earner in non-manual work), respectively.
"We have seen a reduction in salt intake in Britain from 9.5 to 8.1 g per day in the period 2004-2011, thanks to an effective policy which included awareness campaigns, food reformulation and monitoring," said Cappuccio.
"Whilst this is an achievement to celebrate, our results suggest the presence of social inequalities in levels of salt intake that would underestimate the health risks in people who are worse off - and these are the people who need prevention most," he concluded.