Disease burden in Norway in 2016

Material and method

In the following we will briefly describe the operational process in the GBD project, from obtaining health data to producing the final disease burden estimates. Further details can be found in reports from the Centre for Disease Burden at the Norwegian Institute of Public Health (12, 13) and in the most recent Lancet publications, in which the methods are summarised in appendices (6–10). The key disease burden metrics ‘years of life lost’, ‘years lived with disability’ and ‘disability-adjusted life years’ are defined in Box 1.

The GBD project has its own list of diseases and injuries, which is organised hierarchically into four levels and is based on the World Health Organization’s classification of diseases (International Classification of Diseases, ICD). The upper level of the hierarchy comprises three groups: i) communicable, maternal, neonatal, and nutritional diseases (also called group 1 diseases); ii) non-communicable diseases and iii) injuries. There are 21 categories in level 2, while the final level consists of 333 diseases/injuries and groupings of these. The list changes over time and is under continual review. The GBD project collects published and unpublished worldwide health data from sources including population and health registries, health surveys and scientific publications, and calculates mortality, non-fatal health loss and disease burden attributable to risk factors.

The statistical models of the GBD project are designed to generate disease burden estimates for all diseases, injuries and risk factors, for both sexes, all age groups, 195 countries/territories and all years (1990–the present year). Where good national data are available, the GBD estimates will be based very closely on these. Where good data are lacking, the models will ‘borrow’ from other years, age groups or similar countries, so that a complete set of estimates is always generated. Estimates are thus produced even when data are inadequate or missing; this is because the absence of an estimate would otherwise often be taken as evidence that the condition does not cause disease burden and thus does not constitute a health problem (5). The exact data sources used, including the Norwegian ones, can be found in a searchable online database (14). There is often a high degree of uncertainty associated with the disease burden estimates, and the GBD project therefore operates with 95 % uncertainty intervals (UI) for all estimates. New data sources are included each year and the methods are continually refined. All calculations are therefore repeated for all calendar years at each annual update.

Results

The absolute disease burden in Norway increased from 1.16 million disability-adjusted life years in 2006 to 1.21 million in 2016, while the disease burden measured in age-adjusted rates per 100 000 persons decreased by 9 % (95 % uncertainty interval 5–14 %). From 2006 to 2016, the proportion of the disease burden due to years lived with disability increased from 48 % to 52 %, and this proportion was higher in women (57 %) than in men (48 %). Non-communicable diseases accounted for 87 % of the disease burden in 2016, while injuries accounted for 9 %, and infectious, maternal, neonatal and nutritional diseases 4 %.

Non-communicable diseases such as cardiovascular disease, cancer, chronic obstructive pulmonary disease and dementia were responsible for many of the deaths and years of life lost in Norway in 2016, in both women and men (Tables 1 and 2). In both sexes, ischaemic heart disease was by far the most common cause of death, followed by Alzheimer’s disease and other dementias. When calculating years of life lost, deaths that occur at a younger age are assigned greater weight than deaths in old age. Suicide, for example, was ranked in ninth place among causes of death in men in 2016, but was the third most important cause of years of life lost. Deaths due to overdose were also a leading cause of years of life lost in men. In women, breast cancer – which often has a relatively young age of onset – ranked more highly as a cause of years of life lost than of number of deaths. In women, ovarian and pancreatic cancer were also among the ten most important causes of years of life lost. For both of these conditions, however, the 95 % uncertainty intervals overlapped with those for suicide, which was estimated to be responsible for some 6 000 years of life lost among women in 2016.

In general, age-adjusted rates for the leading causes of both death and years of life lost decreased for both sexes over the period 2006–16 (Tables 1 and 2). Ischaemic heart disease and cerebrovascular disease (stroke) showed the largest decreases with respect to both deaths and years of life lost. For men, the number of years of life lost due to lung cancer, chronic obstructive pulmonary disease and suicide also decreased, and for women there was a decrease in deaths and years of life lost due to breast cancer.

Musculoskeletal disorders, especially low back and neck pain, and mental disorders, especially anxiety disorders and depressive disorders (Table 3), were responsible to a large degree for years lived with disability. Diseases of the skin and subcutaneous tissue, sense organ diseases and oral disorders also appeared high on the list for both sexes. Migraine and diabetes mellitus were also key causes of years lived with disability.

There was a consistent increase in the absolute number of years lived with disability in the population over the period 2006–2016, but little change in age-adjusted rates. Exceptions were a reduction in age-adjusted rates for mental disorders due to the use of illegal substances for men, and a reduction in ‘other musculoskeletal disorders’ for women.

The leading causes of disability-adjusted life years in Norway in 2016 were generally similar for men and women (Table 4). Seven of the ten most important disease groups were common to both sexes, including cardiovascular disease, lung cancer, dementia, and low back and neck pain. However, in women, migraine, anxiety and depression were also among the leading causes of disability-adjusted life years, whereas in men, substance use disorders, fall-related injuries and chronic obstructive pulmonary disease were high on the list. In men, only two of the ten leading causes of disability-adjusted life years resulted exclusively from years lived with disability (low back and neck pain, and sense organ diseases), whereas in women five out of ten conditions did so.

Figure 1 shows the distribution, by age, of disease burden in the form of deaths, years of life lost, years lived with disability, and disability-adjusted life years, in 2016. Cancer was an important cause of death from the age of 40–50, whereas cardiovascular disease and dementia dominated in the oldest age groups. Accidents, overdoses and suicides were leading causes of years of life lost in adolescents and adults up to the age of 40, whereas cancer was more prominent for those between 40 and 80 years of age. In Norway, most of those who die, including those who die prematurely resulting in years of life lost, are over the age of 60–70 years. However, the number of years lived with disability is already considerable from the age of 10–20 years and remains high throughout the lifespan. Mental disorders become important from the age of about 10, for example, and musculoskeletal disorders from the age of about 20.

Figure 1 Disease burden in Norway 2016, estimates from the GBD project. All age groups are represented by columns, although not all of these are labelled underneath (e.g. 10–14 lies in between 5–9 and 15–19). Other group 1 diseases = HIV/AIDS and tuberculosis, neglected tropical diseases and malaria, neonatal disorders and others.

Discussion

The disease burden in Norway in 2016 was dominated by non-communicable diseases. Cardiovascular disease, cancer, chronic obstructive pulmonary disease and dementia were leading causes of years of life lost among both sexes. Suicide was also a significant cause of years of life lost, especially for men. Years lived with disability accounted for 48 % of the disease burden in men and 57 % in women. Musculoskeletal and mental disorders in particular were important contributors to this. Although age-adjusted rates for many conditions that lead to years of life lost have decreased over the last ten years, there has been little change in the rates for conditions that primarily result in years lived with disability.

As a result of population growth and ageing, there was an overall increase in the absolute burden of disease in Norway in the period 2006–16, measured in the number of disability-adjusted life years.

However, there was a decrease in the number of years of life lost from cardiovascular disease, which was a major cause of death and years of life lost among both sexes, and the same applied to the age-adjusted rates. This is most likely a result of beneficial lifestyle changes in the Norwegian population in recent years, in addition to progress in the prevention and treatment of cardiovascular disease (19).

For lung cancer and chronic obstructive pulmonary disease, the smoking-related causes of death, the pattern was somewhat different for men and women. There is a long latency from reduced smoking in the population to a visible effect in the form of a reduction in smoking-related causes of death, and there has been a phase shift in the smoking epidemic for men and women (20). For men, the age-adjusted rates for years of life lost to lung cancer and chronic obstructive pulmonary disease fell in the period 2006–16, while there was no definite change in the rates for women. Nor were there any significant changes in the number of years of life lost to lung cancer or chronic obstructive pulmonary disease for either men or women in the period.

The trend in years lived with disability was generally not positive in the period 2006–16. For both men and women, the total number of years lived with disability (non-fatal health loss) due to low back and neck pain, anxiety, depression, fall-related injuries and migraine increased, while the age-adjusted rates were stable. This indicates that the absolute increase may be explained by population growth and/or ageing – not by an increase in illness among people generally. On the other hand, stable age-adjusted rates indicate that we have not become more adept at preventing or treating these conditions, which account for a large and growing proportion of the burden of disease in the Norwegian population.

Despite the fact that women had more years lived with disability than men in 2016, men had a larger total disease burden. Since the reference mortality table used to calculate years of life lost in the GBD project is the same for both sexes, and men generally have a shorter life expectancy than women, men lose more years of life. For example, women and men had approximately the same number of deaths due to ischaemic heart disease in 2016, but women lost significantly fewer years of life because men die of cardiovascular disease at an earlier age than women.

The burden of disease is to a large extent caused by the same disease groups in men and women. Mental and substance use disorders, for example, together accounted for an approximately equal proportion of years lived with disability in men and women, 13 % and 12 % respectively. While anxiety and depression were the predominant causes in women, men were affected to a greater extent by substance use disorders.

One of the major innovations of the GBD project is the fact that it highlights years lived with disability in a population. Conditions that people suffer but do not die from are often invisible in traditional health and cause of death statistics. The disease burden from such conditions is analysed in various ways in different academic communities and disciplines, and this makes cross-comparisons very challenging. The GBD project attempts to quantify years lived with disability using one shared methodology, so that they can be measured on the same scale as years of life lost. It may well come as a surprise to many that a little more than half (52 %) of the disease burden in the Norwegian population in 2016 could be ascribed to years lived with disability.

Conclusion

The GBD project is an international epidemiological project. Estimates of the burden of disease, injury and risk factors for the years from 1990 onward are updated annually, for 195 countries and territories worldwide, for both sexes and all age groups. This provides an overview of the health of populations which in practice is impossible to obtain for any single country alone. In 2016, the burden of disease in Norway was dominated by non-communicable diseases such as cardiovascular disease, low back and neck pain, cancer, dementia and mental disorders. Although the last decade has shown positive developments for conditions that lead to years of life lost, particularly for cardiovascular diseases, the same trend has not been observed for conditions that generally result in years lived with disability.