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| Epidemiology of diabetes mellitus in the north Mediterranean countries |
Michele Dalla Vestra, Gaetano Crepaldi
Department of Medical and Surgical Sciences, Clinica Medica I, University
of Padova, Italy
Although the projections of a large increase in the prevalence rates of
diabetes are concordant, there are discrepancies in the actual rates in
some countries (1). It is extremely difficult to describe the epidemiology
of diabetes in Europe, since there are no national registries available
to assess the number of patients with type 1 or type 2 diabetes. Prevalence
of diabetes in adults worldwide was estimated to be 4% in 1995 and it will
increase sharply in the future (2). Between 1995 and 2025 the adult population
will increase by 64%; the prevalence of diabetes in adults will increase
by 35%, and the number of diabetic patients will increase by 122%. For the
developed countries there will be an 11% increase in the adult population,
a 27% increase in the prevalence of adult diabetes, and a 42% increase in
the number of diabetic patients. For the developing countries there will
be an 82% increase in the adult population, a 48% increase in the prevalence
of adult diabetes, and a 170% increase in the number of diabetic patients
(2). Prevalence is higher in developed than in developing countries and
will remain so until 2025, although the proportional increase will be greater
in the developing countries. Thus diabetes, especially type 2, is evolving
as a major health problem in both developed and developing countries.
Type 1 diabetes
The incidence of type 1 diabetes in children younger than 15 years of age
has been extensively reported, but few data, and none from Europe, are currently
available on the incidence of type 1 diabetes in older age groups. In the
Mediterranean and neighboring areas the incidence rates of type 1 diabetes
under the age of 15 years show wide variations. In Italy the incidence of
type 1 diabetes in children aged 0-14 years is 6-11.7 (per 100 000 per year),
while in Sardinia the incidence is 34.4, one of the highest in Europe (3).
In general, the highest incidence is among subjects aged 10-14 years and
the lowest in children aged 0-5 years for both genders. However an earlier
incidence peak in children aged 5-9 years is a common feature of insular
Italian areas, but not of Northern Italy (3). In France, Levy-Marchal showed
that the annual diabetes incidence rates for 1988 and 1995 were 7.17 and
9.28 per 100,000, respectively; this study included 2 million subjects younger
than 20 years of age (4). Similar results have been reported in Spain (8-10.9
per 100 000 per year), in Croatia and Slovenia (7.2 and 7.6 per 100 000
per year, respectively) (3). The incidence in the Mediterranean countries
is different from the incidence in Northern Europe; indeed in Finland, Tuomilehto
et al reported that for children younger than 14 years, the annual incidence
rate in 2000 was 45 per 100 000 (5). In contrast with other European countries,
the incidence of the disease in the Mediterranean area does not follow any
geographical pattern.
Probably differences in environmental factors, genetic susceptibility or
both are important for such a wide variation. The environmental risk factors
identified so far can be classified into 3 main groups: diet, toxins and
viral infections. Concerning diet, cow's milk consumption has been shown
to be associated with increased incidence of type 1 diabetes (6). Parslow
RC et al (7) found that also nitrate concentration in drinking water positively
associates with incidence of type 1 diabetes. Different incidence may also
be related to viral epidemics or to differences in the virulence of viruses
(8). As in other areas of the world, variation in incidence appears to be
related to ethnicity, demonstrating the importance of the differential genetic
susceptibility in different populations. Indeed Sardinians, who have the
highest incidence of type 1 diabetes, together with Finns, in the world, show
a high frequency of HLA haplotypes implicated in type 1 diabetes susceptibility
and paucity of protective alleles when compared with other Caucasian populations
(3). Moreover, the interactions between different genes and environmental
factors may be important, as suggested by some studies performed in Israel.
In contrast, studies in Sardinian migrants showed that the high incidence
of type 1 diabetes is a consequence of their genetic background more than
of environmental influences (9). This does not mean that environmental factors
are not relevant in the etiology of type 1 diabetes, but rather that environmental
triggers may have a major impact on genetically predisposed subjects. Worldwide
a female excess is found in low-incidence populations while the reverse
is true in several of high-incidence populations. In the Mediterranean countries,
the male to female ratio is close to 1.
Type 2 diabetes
Type 2 diabetes is the major component of the worldwide diabetes epidemic.
King et al (2) reported that the prevalence of diabetes in adults aged
20 years and over was 7.5% in 1995, 7.8% in 2000 and will be 10% in 2025
in Italy. Also in Spain the prevalence of diabetes will rise from 7.2% in
1995 to 9.5% in 2025. In contrast, the same authors reported that in France
and in Croatia there will be only a moderate increase in the prevalence
of diabetes in the adult population: from 2.1% in 1995 and 2000 to 2.6%
in 2025 in France and from 4.4 to 5.1% in Croatia (2). In these countries,
as in all developed world, the majority of people with diabetes is aged
³ 65 years. This study was based on 5-year age and sex specific prevalence
rates, from rural and urban areas of various countries. Inclusion criteria
were: diagnosis of diabetes made according to the recommendations of WHO
expert groups (plasma venous concentration of 11 mmol/L 2 h after a 75 g
oral glucose challenge).
There are many factors influencing the increasing prevalence of diabetes.
In so-called developed countries, diabetes, especially type 2 diabetes,
has evolved as a major health problem, because of increasing life expectancy
and because of changes in lifestyle and diet, with increased prevalence
of obesity. Industrialization and socioeconomic development are certainly
the most important determinant of the diabetic epidemic in developing countries,
where improved nutrition, better hygiene, the control of many infectious
diseases, and new effective treatments have resulted in increased longevity
(10).
In the western world, people are living longer but the birth rate is stable.
This ageing of the population will itself mean that more people will develop
diabetes. Thus, age is an important variable influencing the prevalence
of diabetes. Most epidemiological studies show that the prevalence of type
2 diabetes increases with age and then declines in very old people (10).
However, recent observations have also shown that there is a large percentage
of undiagnosed diabetes in older people. There is also evidence that diabetes
is more common in females than in males, although in recent years a greater
increase in men diagnosed with diabetes has been observed. As diabetes is
an age-related disorder, countries with elderly populations have more diabetes
than developing countries with younger populations. The high prevalence
of type 2 diabetes depends especially on the high prevalence of obesity.
In more than 80% of cases, type 2 diabetic patients are obese and therefore
interventions towards reduction in diabetes incidence should be carefully
planned in terms of prevention of modifiable risk factors. Not only diet
is important, but also the sedentary lifestyle is thought to play an important
role in increasing the prevalence of type 2 diabetes, especially in young
people (10). Recent evidence showed that diabetes can be prevented in the
high risk group of people with impaired glucose tolerance by exercise and
diet, confirming the importance of these environmental factors in the etiology
of type 2 diabetes (11).
Moreover, several studies have found significantly higher prevalence rates
in urban rather than rural environments within the same country. Comparisons
of migrant populations living in rural and urban settings in the same country
also show an excess of diabetes in urban communities. This aspect is actually
very interesting since we witness an important migratory flow from developing
countries to Europe.
Since both the prevalence of type 2 diabetes and the mean age of patients
are increasing throughout most European countries, there has been a consequent
increase in the prevalence of cardiovascular and microvascular complications.
Recent intervention trials showed that improved glycemic control and aggressive
treatments of hypertension and hyperlipidemia can significantly reduce the
risk of macrovascular and microvascular complications (12, 13).
The CODE-2 study was conducted to evaluate the health care costs of people
with type 2 diabetes in Europe. In Italy, the yearly medical costs for outpatients
care and hospitalization per patient was 525 and 2173 Euro respectively
in 1998 (4). Moreover this study showed that costs associated with treatment
of type 2 diabetic patients with either micro or macrovascular complications
were twice the costs of diabetic patients with no complications. The presence
of both complications increased costs more than three-fold.
In conclusion, although there is a paucity of data reported for the European
countries, estimates and projections suggest an epidemic expansion of diabetes
incidence and prevalence in all European countries. Knowledge of prevalence
of diabetes and identification of risk factors are essential for a rational
planning of health services, to improve the organization and cost-effectiveness
of health care.
Suggested readings
1) King H, Rewers M. Global Estimates for Prevalence of Diabetes Mellitus
and Impaired Glucose Tolerance in Adults. Diabetes Care:1993;16:157-176.
2) King H, Aubert R, Herman W. Global Burden of Diabetes, 1995-2025. Diabetes
Care.1998;21:1414-1431.
3) Muntoni S, Muntoni S. New Insights into the Epidemiology of Type 1 Diabetes
in Mediterranean Countries. Diabetes Metab Res Rev.1999;15:133-140.
4) Passa P. Diabetes trends in Europe. Diabetes Metab Res Rev.2002;18:
S3-S8.
5) Tuomilehto J, Karvonen M, Pitkaniemi J, Virtala E, Kohtamaki K, Toivanen
L, Tuomilehto-Wolf E. Record-high incidence of Type 1 (insulin-dependent)
diabetes mellitus in Finnish children. The Finnish Childhood Type 1 diabetes
Registry group. Diabetologia.1999;42:655-660.
6) Gerstain HC. Cow's milk exposure and type 1 diabetes. Diabetes Care.1994;17:13-19.
7) Parslow RC, McKinney PA, Law GR, Staines A, Williams R, Bodansky HJ.
Incidence of childhood diabetes mellitus in Yorkshire, northern England,
is associated with nitrate in drinking water: an ecological analysis. Diabetologia.1997;40:550-556.
8) Szopa TM, Titchener PA, Portwood ND, Taylor KW. Diabetes mellitus due
to viruses- some recent developments. Diabetologia.1993;36:687-695.
9) Muntoni S, Fonte MT, Stoduto S. et al. Incidence of insulin-dependent diabetes
mellitus among Sardinian-heritage children born in Lazio region, Italy.
Lancet.1997;349:160-162.
10) Gadsby R. Epidemiology of diabetes. Advanced Drug Delivery Reviews.2002;54:1165-1172
11) Tuomilehto J, Lindstom MS, Eriksson JG, Valle TT, Hamalainen HH, Hanne-Parikka
P. Prevention of type 2 diabetes by changes in lifestyle among subjects
with impaired glucose tolerance. N Eng J Med.2001;344:1343-1349.
12) UK Prospective Diabetes Study Group. Intensive blood glucose control
with sulfonylureas or insulin compared with conventional treatments and
risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet.1998;352:837-853.
13) Gaede P, Vedel P, Parving HH, Pedersen O. Intensified multifactorial
intervention in patients with type 2 diabetes mellitus and microalbuminuria:
the Steno type 2 randomized trial. Lancet.353;617-622,1999. |
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