An increase in the number of obese individuals has been recorded all over the industrialized world, while showing a progressive pattern also in developing countries. According to the latest data from 2015, there were more than 603 million obese adults and more than 107 million obese children in the world, the figures almost double those recorded in the 1980s (1).

Body mass index (BMI, kg/m²) has been used as a measure to define obesity, whereby a BMI greater than 25 kg/m² denotes overweight and BMI greater than 30 kg/m² denotes obesity. Using BMI to define and study the prevalence of obesity is convenient and simple; however, the distribution of body fat, i.e. the amount of visceral fat, has been found to be a better indicator for assessment of the association of obesity and unfavorable health outcomes. There is visceral and subcutaneous body fat, and the waist to hip circumference ratio is the simplest indicator of visceral fat.

Current research into the prevalence of obesity in European countries suffers from some methodological problems such as using non-representative samples, being conducted in only a few European countries, and employing non-standardized anthropometric measures that are difficult to interpret. A study carried out in 2010 in 16 European countries (2) was designed as a cross-sectional survey and included 14,685 subjects older than 18. The results obtained showed that 34.8 % of adults were overweight and 12.8 % were obese; accordingly, nearly half of the study subjects (47.6 %) were overweight or obese. Croatia is a country with with a very high prevalence of overweight and obese subjects (58.2 %), second only to Hungary. Croatia is the leading country in the prevalence of obesity of 21.5 %, as assessed on a study sample. The prevalence of obesity is lower in western and south Europe countries as compared with the central, eastern and north Europe countries (Figure 1). The prevalence of overweight and obesity increases with age and decreases with higher level of education.

In comparison with the United States of America (USA), the prevalence of obesity in Europe is less than half the prevalence recorded in the USA (14.0 % vs. 35.5 % in males and 11.5 % vs. 35.8 % in females).

It should be noted that this was a survey in which the participants self-reported their body weight and height, and no measurements were performed. However, the potential biases and socially desirable answers probably did not differ considerably among various countries; even if absolute data on the prevalence of obesity are not precise enough, obesity in Croatia as compared with other European countries obviously poses a major public health problem.

According to the recently published results of the European Health Interview Survey (EHIS) (3) conducted in 2014-2015 on the European Union (EU) population older than 15, in which Croatia also took part, 15.7 % and 34.5 % of the EU population are obese and overweight, respectively. Data on Croatia are even worse than this mean prevalence, i.e. 18.0 % of the Croatian population are obese and 37.7 % overweight, while 41.9 % have normal body weight. Overweight and obesity are more prevalent in males than in females (Figure 2) (4). It should be noted that the nutritional status was calculated according to anthropometric data reported by the participants.

Based on the Croatian Health Survey conducted in 2003 on a representative sample of the population older than 18, more than half of women and two-thirds of men are overweight (BMI >25 kg/m²; 54.3 % of women and 63.2 % of men). Every fifth adult is obese (BMI >30 kg/m²; 20.6 % of women and 20.0 % of men); and one-third of women and nearly half of men are overweight (BMI 25-30 kg/m²; 33.7 % of women and 43.0 % of men) (5).

Data derived from a sample of 3229 subjects included in the Croatian Health Survey 2003 and then in the CroHort study 2008 yielded the mean annual increase in the prevalence of obesity of 10.6 % in men and 11.08 % in women during the 5-year period between the 2 surveys. The cumulative incidence of obesity in this 5-year period was higher in women (20.5 %), whereas in men it was 8.7 % (6).

Obesity in children is also increasing all over the world. In 2014, 41 million children younger than 5 years were obese or overweight (7). Overweight children are at an increased risk of developing cardiovascular disease, type 2 diabetes mellitus, sleep disorders and asthma, and they frequently have problems associated with being overweight in adulthood. The latest international survey of health behavior in schoolchildren (Health Behavior in School-aged Children 2013-2014) (8), also carried out in Croatia (9), included 42 countries and collected data on children aged 11, 13 and 15 years. In Croatia, the proportion of male schoolchildren with BMI exceeding the arithmetic mean value amplified by 1 standard deviation decreased with age, from 33 % in 11-year-old through 27 % in 13-year-old to 24 % in 15-year-old children, and this decrease was even more pronounced in female schoolchildren, with the respective figures of 20 %, 14 % and 9 % (Figure 3).

Concerning the group of 11-year-old children, Croatia ranks 11^th country by the proportion of schoolchildren with BMI exceeding the arithmetic mean by 1 standard deviation. In case of the 13-year-old and 15-year-old children, Croatia ranks 14^th and 20^th country, respectively. Results recorded on the 11-year-old children according to gender in the selected countries included in the study are shown in Figure 4.

According to the abovementioned study of the impact of obesity on the global disease burden, in 2015 there were 4 million deaths worldwide that were at least in part caused by high BMI, accounting for 7.1 % of all-cause deaths. In addition, obesity contributed as a causative agent to 120 million disability-adjusted life-years (DALY), another measure of the global disease burden. As many as 39 % of deaths associated with high BMI and 37 % of DALYs occurred in individuals with BMI lower than 30 (1).

Cardiovascular diseases are the leading cause of deaths and DALYs associated with elevated BMI (52.4 %), while CKD ranks second as a cause of DALYs due to increased BMI (24.4 %) (1).

Obesity is one of the major risk factors for development of CKD. Besides its indirect effects as the cause of diabetes mellitus and arterial hypertension that subsequently influence development of CKD, obesity has been demonstrated to act also as an independent risk factor for CKD. In overweight individuals, compensatory hyperfiltration occurs to enable the body to cope with the increased metabolic requirements. This in turn results in increased intraglomerular pressure, which may lead to kidney damage and at long term to the development of CKD. The amount of visceral fat in the body has been shown to be a risk factor for development and poorer outcome of CKD independently of BMI (10). Obesity doubles the risk of CKD relative to the normal nutritional status. Overweight is associated with an increased risk of renal calculi and kidney carcinoma (11).

Chronic kidney disease currently is a major public health problem due to its ever-growing prevalence, and consequentially for the increasing need of renal replacement therapy (RRT) with dialysis and transplantation. It is estimated that about 10 % of the European population suffer from CKD (12). Treatment by RRT is associated with lower quality of life and life expectancy in these patients, as well as great financial burden upon the society. In industrialized countries, dialysis and transplantation impose huge financial burden, which will become unsustainable considering the steady increase in the number of these patients. The increase in the prevalence of CKD certainly is caused by the population aging, increase in the prevalence of diabetes mellitus, as well as uncontrolled arterial hypertension, obesity, excessive and unreasonable use of nonsteroidal anti-inflammatory drugs, and exposure to various environmental toxins.

Chronic kidney disease can be classified according to stages defined by the Kidney Disease Outcomes Quality Initiative (KDOQI). There are 5 stages as determined by the estimated glomerular filtration rate (eGFR) and indicators of the kidney structural changes (e.g., proteinuria) (13). CKD stages 3, 4 and 5 can be detected solely by eGFR determination, whereas detection of earlier CKD stages 1 and 2 also requires determination of urine albumin. CKD causes metabolic, endocrine, neurologic and cognitive disorders, as well as renal failure, and is a cardiovascular risk factor, whereas CKD complications involve all the organ systems in the body.

In recent years, the association of CKD with cardiovascular morbidity and mortality has been ever better understood. Several large studies have shown that the risk of myocardial infarction or stroke in association with CKD outweighs the risk of initiating RRT. Unfortunately, the presence of CKD is frequently asymptomatic, and it is only recognized in advanced stages when the cardiovascular risk is even higher. According to some estimates, after control of other cardiovascular risk factors has been achieved, CKD increases this risk twofold to even fourfold (14). In addition, in CKD stages 1 and 2 the cardiovascular risk is identical to the risk associated with CKD stage 3, emphasizing the importance of early detection of the disease and increasing cost-effectiveness of the CKD screening programs (12).

Chronic kidney disease in early stages is free from symptoms and therefore frequently unrecognized; that is why it is quite difficult to collect reliable data on its true prevalence.

A recent meta-analysis aiming at assessment of the global prevalence of CKD included data from 100 studies conducted in 112 different populations. The estimated global prevalence of CKD in all studies was 13.5 % (based on data on 44 populations), whereas the estimated prevalence of CKD stages 3-5 was 10.6 % (based on data on 68 populations). Data on the CKD prevalence according to stages in all the studies involved in the analysis yielded a prevalence of 3.5 % for stage 1, 3.9 % for stage 2, 7.6 % for stage 3, 0.4 % for stage 4, and 0.1 % for stage 5 (13).

Regression analysis of the correlation of CKD prevalence with age, arterial hypertension, diabetes mellitus, obesity, mean BMI and smoking habit showed positive correlation of CKD with older age, hypertension and diabetes mellitus in most of the study populations. Obesity and mean BMI were not significantly associated with CKD prevalence, whereas smoking habit showed negative correlation (however, the latter was annulled by excluding an outlier study where the low cut-off for defining smokers resulted in as many as 69.1 % of smokers in the sample) (13).

Gender distribution shows the prevalence of CKD to be higher in women. In the studies involving all CKD stages, the prevalence was 12.8 % and 14.6 % in men and women, respectively. In the studies on CKD stages 3-5, the respective figures were 8.1 % and 12.1 % (13).

There are no data on the prevalence of CKD in Croatia but the magnitude of the problem can be illustrated by use of indicators derived from routine healthcare and mortality statistics. Diseases of the urinary and sexual systems rank ninth by the number of deaths with 1072 dead patients in 2015, of which 494 patients died from renal failure (Table 1). The same group of diseases ranks seventh by the number of hospitalizations with 36,542 hospitalizations, of which 6605 hospitalizations were due to renal failure (Table 2). This group of diseases ranks fourth by the number of diseases and conditions recorded in family medicine offices with 597,997 cases, accounting for 5.3 % of the diseases and conditions established at primary healthcare level, of which 13,859 cases were diagnosed with renal failure (Table 3). It should be noted that data on diseases and conditions recorded at primary healthcare level cannot be used for determination of particular disease prevalence but only for providing an insight into the frequency of healthcare utilization at the primary healthcare level for a particular disease or condition.

According to the results of EHIS (4) conducted in Croatia in 2014-2015 on a population older than 15, kidney problems were reported by 3.2 % of male and 5.6 % of female subjects. Data on renal diseases were collected from participant reports on having suffered from some of these diseases in the past 12 months.

According to data from the Croatian Register of Renal Replacement Therapy, at the end of 2014 there were 4102 persons in Croatia on RRT, which was by 4.3 % less than the year before. The share of patients with kidney transplant has increased by 5.2 % as compared with previous year, whereas the percentage of hemodialysis patients has been on a decrease since 2007. The population on RRT is on increase because of the growing number of transplanted patients, despite reduction in the number of patients treated with hemodialysis and peritoneal dialysis (15).

An alternative to the epidemic of CKD, advanced forms of renal insufficiency and increased mortality is early detection of CKD and use of preventive and therapeutic measures to slow down or halt progression of the disease. Detecting the disease in its early stages allows for its timely control while reducing the likelihood of chronic renal failure and the need for dialysis and kidney transplantation (12).

Some European countries have developed programs of early CKD detection, but they vary in the diagnostic methods used, borderline eGFR values employed, and populations involved. In these programs, the most common target groups are diabetic patients, elderly, and those with hypertension. However, a pitfall of this approach is that, according to some estimates, per each individual diagnosed with hypertension or diabetes mellitus there is another one in whom hypertension or diabetes mellitus has not yet been diagnosed but has already caused damage to the organs (12). Employing eGFR as the only diagnostic method is of no use in detecting individuals in early stages of the disease when timely intervention is of crucial importance to prevent progression of the disease. In fact, the prevalence of CKD is highest in the first three stages of the disease, whereas eGFR determination can only detect ≥stage 3 CKD. Therefore, follow up determination of albuminuria should also be included in the CKD screening programs. According to the study that assessed the results of CKD screening programs in Norway, The Netherlands and Spain, the prevalence of pooled CKD stages 1 and 2 ranges from 5.1 % to 7 %, of stage 3 it is 4.5 %–5.3 %, and of stage 4 it is 0.1 %-0.4 % (12). It is also necessary to perform education and to increase population awareness of the CKD problem, as well as of the risk factors and possibilities of prevention, in particular among the groups at risk. Special emphasis should be put on education about healthy lifestyles as primary prevention, so that the disease would not develop at all.

Overweight and obesity, as well as the disease they cause, are preventable to a great extent; however, favorable results in halting the epidemic of obesity are hard to achieve irrespective of the ever better knowledge and options currently available. The problem of obesity cannot be solved at the level of the individual and healthcare system but at the level of society as a whole, in particular food industry and environment sustaining healthy lifestyle. The countries where comprehensive and systematic programs of prevention of obesity and other risk factors have been implemented for years have lower morbidity and mortality rates of the most common chronic diseases.

Systematic performance of the programs of prevention firstly requires legal and strategic healthcare policy documents. Concerning obesity, Croatia has passed a series of strategic documents; however, some crucial documents have not yet been enacted. Action plan for the prevention and reduction of overweight was passed for the 2010-2012 period, so currently there is no plan of prevention and control of obesity in Croatia. National guidelines for the nutrition of elementary school children were enacted in 2013, however, there is no surveillance of its implementation, whereas the planned national guidelines for the nutrition of working population are still in the preliminary phase. In 2014, the Živjeti zdravo (Living Healthy) national program was launched, consisting of the following components: health education; health tourism; health and diet; health and work place; health and environment; and a network of the Živjeti zdravo (Living Healthy) centers for health promotion, including those on appropriate diet and physical activity. A proposal of the action plan for prevention and surveillance of chronic non-communicable diseases has been designed, including control and prevention of the risk factors such as unfavorable dietary habits and obesity; however, this action plan has not yet been enacted.

Studies of the prevalence of physical (in)activity conducted in Croatia indicate that about 60 % of the adult population are not involved in any form of physical activity. In spite of the great public health problem posed by physical inactivity in Croatia, no strategic documents to provide preconditions for efficient efforts and promotion in the area have been enacted so far.

Accordingly, it is concluded that some relevant strategic documents to enable systematic implementation of the program of prevention and early detection of chronic diseases are lacking at the national level, and so are the respective human and financial resources to ensure necessary capacities for its implementation.