Cardiovascular disease and high blood pressure trend analyses from 2002 to 2016: after the implementation of a salt reduction strategy

Cardiovascular disease (CVD) is the leading cause of death around the world [1]. An estimated 4 million people in Europe die by CVD annually [2]. However, many of the CVD events could be prevented if we focused on modification of the main risk factors [3].

In 2010, high blood pressure (HBP) was the leading risk factor contributing to global disease burden, accounting for more than 15% of all health loss in adults [4], and responsible for 62% of all strokes and 49% of ACS events [5]. Although sodium is an essential nutrient necessary for maintenance of plasma volume, acid-base balance, transmission of nerve impulses, and normal cell function [6], current salt consumption is much greater than needed for survival, creating an overload on the metabolic system [7]. This overload can increase blood pressure (BP) [8]. Increased salt consumption is estimated to have caused millions of deaths, mostly related to CVD, particularly stroke, which is the leading cause of death in Portugal [9], being one of the countries with the highest mortality rates by stroke among the Western countries [10]. The high prevalence of HBP is pointed to as one of the main reasons.

Implementing both population-wide and high-risk approaches to reduce blood pressure seems almost inevitable due to the large burden of HBP [11, 12]. Even small reductions of HBP prevalence in the population could lead to great health gains. Knowing the importance of these approaches, the World Health Organization (WHO) created a set of recommendations to reduce dietary salt to 5 g/day, in order to prevent chronic disease and improve health [13]. In the European Union, 26 out of the 53 Member States, including Portugal, implemented operational salt reduction policies including laws aiming to reduce salt intake. Recent reports have shown that salt consumption in Portugal has been declining in recent decades to a minimum of 7.3 g/day in 2016 [14]. Prospective studies have shown that reducing salt intake can lead to reductions in blood pressure and, eventually, to a reduction in CVD events [15].

By 2010 a set of public health initiatives were implemented in Portugal, namely a reduction in salt added to bread and mandatory salt labelling in pre-packed food. As these initiatives are meant to reduce salt intake we hypothesized that it could lead to a reduction in the proportion of HBP and CVD, namely ACS and stroke. Therefore in our study, we aim to assess the trends in the proportion of HBP in ACS patients, as well as the trends in stroke and ACS in the country, before and after these initiatives were applied. For the sake of clarity in our study we refer as salt for all sodium data.

A total of 43,271 ACS events were registered in the NRACS over the last 14 years. The proportion of males presenting with ACS has been consistently higher than women, with around 69% of ACS events occurring in males. Mean age through the years of study has also been fairly steady, ranging from 65 to 66 years old (Table 1). Male/female ratio for HBP patients (Fig. 1) has also remained fairly steady through the years in the ACS population.

The proportions of patients with HBP ranged from a minimum proportion of 50.0% to a maximum of 79.2%.

Breakpoint analysis revealed an estimated breakpoint around the year 2013 for the proportion of HBP patients (Fig. 2), the year after there is a decreasing trend, however it was not significant (p-value = 0.832). Analyses showed the trend before 2013 was, in fact, increasing and started to decrease after this year (β_before = 0.009, CI: 0.007, 0.011; β_after = − 0.003, CI: -0.037, 0.0302). Although zero is present in the CI for the slope after 2013, the change between both slopes (before and after 2013) is negative with a decrease of − 0.012 in the monthly proportion. Thus, the decrease estimated after 2013 is higher than the increase estimated before 2013. This decrease in proportion can be translated into a reduction of 555 people per year presenting with HBP in the ACS population (Table 2).

Figure 3 displays the frequency of ACS and stroke admissions from 2002 to 2016. A total of 115 public hospitals from mainland Portugal registered ACS admissions from 2002 to 2016 and 122 registered stroke admissions. A maximum age of 99 years old was found in the database and the majority of admissions were for both ACS and stroke.

We analysed trends for ACS and stroke and tested the significance for a breakpoint in the year 2013.

Although none of the remaining trends were significant (Table 2) for ACS crude rates (β = − 0.057, CI: - 0.154, 0.039) and stroke crude rate (β = − 0.049, CI: -0.128, 0.029), a decreasing trend can be observed.

The seasonal pattern observed for ACS and stroke was consistent with that reported elsewhere [21], with higher rates of admission over winter, and lower rates during the summer (Fig. 3).

Our results showed increasing trends in the proportion of HBP comorbidity in the ACS population until 2013, the following years the trends appear to decrease. This year was used as a breakpoint to test for differences in trends for ACS and stroke. Decreasing trends for both outcomes were also found, but were not significant.

Although our results were not statistically significant, and thus must be interpreted with caution, it is encouraging to find decreasing trends, especially in the proportion of HBP patients in the ACS population, with a reduction of nearly 600 people per year, after the implementation of a major public health measure that was meant to reduce salt intake.

Even a small reduction in the proportion of HBP in the ACS population, as the one observed in our study of 555 persons per year achieved through a population-wide approach, can have huge impacts [22, 23]. This impacts has effectively slowed down the development of atherosclerosis in young people, thereby reducing the likelihood of future epidemics of CVD [24].

The decreasing trend for ACS was observed for women but not in men, in fact salt intake have been previously link to higher risk of CV events in women but not in men [25], more particularly studies have found that women could benefit more, concerning stroke reduction, from dietary salt reduction than men [26].

As salt sensitivity is known to be greater in the elderly we hypothesized that if the salt reduction law could have some effect it would be greater for the elderly [27, 28]. In fact our results suggest a decreasing trend for all outcomes in the older group.

Results from this type of population-wide approach were seen in the UK, where salt reduction campaigns showed significant results, achieving a 15% salt reduction from 2003 to 2011, which translated into about 6000 fewer deaths from CVD, saving about 1.5 billion pounds a year [8].

The decreasing trends for all of our outcomes was not as great as we expected, however the fact that the starting of the decrease takes place after the implementation of these approaches, and the trend of HBP in ACS patients was steadily increasing before that, supports our hypothesis that this approach of reducing salt in bread and making pre-packed salt labelling mandatory can influence HBP prevalence in ACS patients as well as CVD trends.

The fact that, salt intake levels have been decreasing in Portugal to the most recent value of 7.3 g/day in 2016 [14] also supports our hypothesis of the potentially effect of the regulation applied in the country. Although this value was obtained by a 24 h dietary recall questionnaire [29], these values were validated against urinary sodium excretion for a sub-sample of 100 subjects and the values were highly correlated.

In addition, BP levels have been declining in the Portuguese population, from a mean BP of 134.7/80.5 mmHg in 2003 [30] to a mean BP of 127/74.6 mmHg in 2012 [10].

Furthermore, several studies showed that bread is one important source of salt in Portugal [7], and contributes to about one-sixth of daily salt intake [7]. Results from the National Food, Nutrition and Physical Activity Survey suggest most of the salt consumed by the population comes directly from bread and toast, charcuterie products, and soups [14]. It was all this evidence that led to the creation of the regulation to reduce salt in bread to a minimum of 1.4 g of salt per 100 g of final product [31] and mandatory labelling for pre-packed products stating clearly the salt content of the product. Portugal was, thus, the first western country to create a law for the clear definition of the quantity of salt contained in bread.

Besides the legislation in 2010, several initiatives have been carried in Portugal to reduce salt intake, such as: electronic tools, such as websites included in the National Program for the Promotion of Healthy Eating, to free distribution of books and brochures, by the creation of an animated series, and the creation of the National Food, Nutrition and Physical Activity Survey, aiming to collect nationwide data on dietary intake and physical activity [14].

There is already evidence that reducing salt intake could reduce BP in the Portuguese population. One community intervention trial conducted in Portugal demonstrated that reducing salt intake in an entire village, including cooking and processed food, led to a significant reduction in the BP of the population [32].

Policy interventions to reduce national sodium consumption have demonstrated to be highly cost effective in nearly every country in the world. These interventions could reduce millions of disability adjusted life years at low cost and be more cost-effective than pharmacological interventions [26, 33].

Policy and system changes are critical to reduce HBP in populations, including legislation and public education to reduce dietary sodium and food pricing policies, to support prevention and management of CVD [34].

Alternative public health approaches, such as reducing salt in processed foods and bread, and labelling of processed food along with the use of multiple fiscal and educational policies, have already been proposed by the WHO as the first-line approach for CVD reduction, when implemented on a wide scale [24, 34].

In spite of several efforts being made in the country to reduce salt intake, there is still room for improvement, namely in food labelling [35], adjusting it to the level of health literacy in the country. Once the level of health literacy in Portugal was slightly lower than the rest of European countries [36], this might have prevented the population from fully benefiting from the labelling, as the interpretation of salt content in each food can be difficult.

Simpler labelling systems already exist in other countries, such as labels that rely on the use of front-of-pack information such as logos with information on the overall healthiness of the food and traffic light and colour coding systems, which might help citizens make healthier choices. Countries such as Finland and the UK have already implemented some of these labelling systems. In Finland, food products with salt contents below the designated levels display a low-salt label to emphasise their lower-than-conventional salt levels [37]. In the UK, a traffic light system to distinguish between high, medium, and low salt content in food products was implemented. These strategies proved to be efficient in reducing salt intake in the population [38]. The traffic light labelling system has been proposed by the Portuguese Hypertension Society to help the population choose products regardless of their level of literacy.

More restrictions are being planned in Portugal to further reduce salt intake, such as a taxes on products with more than 1 g of salt per 100 g of finished product such as: pre-packaged crackers and biscuits; pre-packaged cereal flakes and pressed cereals; and pre-packaged, dehydrated potato chips. A rate of 0.80 Euros per kilogram of finished product will be applied to these products.

On the other hand, further reduction of salt content in bread, to a minimum of 1 g per 100 g of final product, was proposed to be achieved by 2020, with continuous reductions each year after 2018.

Our study presents encouraging indications suggesting there have been reductions in the proportion of hypertensives among ACS patients after 2013, along with an annual decrease in the rates of ACS and stroke.

In conclusion, the fact that we found decreasing trends for both HBP in ACS patients and CVD outcomes after major initiatives to reduce salt intake were implemented in the country, suggests that this type of approaches, although hard to measure, can impact the trends of major public health outcomes. Thus, this research is relevant to the public health community because it provides an indication about the impact that a population-wide approaches can have on CVD risk factors, and CVD trends themselves. Our results suggest that population-wide approaches can have an impact on the prevention and improvement of CVD control, reducing the number of CVD events and eventually reducing premature death, morbidity, and disability by CVD. Our study also highlights the importance of measuring the impact of these types of initiatives. These findings stress the need for public health policy in CVD to improve the health of populations addressing, in the first place, the well identified risk factors for CVD.

Undoubtedly, more studies are needed to assess the impact of such measures, not only for other diseases beside CVD, but also adding more years to the study would allow analysis of long terms effects of the public health initiatives. On the other hand, as more restrictions on salt intake are being planned in Portugal, in the next years it is very relevant to assess what is the current panorama and what further reductions we can expect.