It is well known that age is the primary risk factor for developing all types of dementia. The prevalence of dementia increases proportionally with age and doubles every 5 years, starting from 1% between 60 and 64 years of age through 21% between 85 and 90 years, up to 40% in the group of 90-94 years old (1, 2). Consequently, it might be suspected, that almost all persons aged 100 and over should be endangered by dementia. However, the above studies did not cover persons over 95 as a separate group due to very small sample sizes. Moreover, not all results of studies on the prevalence of dementia in the oldest old support the assumption of linear increase in dementia prevalence with age. Some studies have shown that the prevalence of dementia in the age group of over 95 rises to 60-70% (3, 4). In other studies, it has been proved that the prevalence increases up to the age of 90 years, then it starts to decline in persons aged 90-94, and reaches a plateau of 40% beyond the age of 95 years (5, 6).

Due to the fact that, until recently, centenarians have been very rare, centenarian studies were infrequent in the past. Along with the increase of centenarian population in recent years, a number of centenarian studies have investigated the prevalence of dementia. These studies reported dementia prevalence rates ranging from 30 to 100% (7, 8).

In Poland, available epidemiological data on the prevalence of dementia concern exclusively age groups between 65 and 84 years (9).

The aim of the present study is to assess the occurrence and severity of dementia in individuals aged 100 years and older.

This study forms a part of the Polish Centenarians Program “Environmental and genetic factors of longevity of Polish centenarians”. All centenarians were identified through the Polish General Electronic System of Population Registration. Age was verified based on birth certificates or other significant documentation or sometimes indirectly e.g. through the children’s age or the time of military service. All participants were initially contacted by post and then by telephone. All centenarians who consented to participate in the Program were visited in their homes (including nursing homes) by geriatricians. The examination record included a very detailed interview on sociodemographic features, medical history, general physical examination, simple assessment of sight and hearing, and blood tests, including serum vitamin B12 and folic acid levels.

One hundred and thirty five eligible centenarians residing in Warsaw area were contacted. Thirty three of them refused to participate in the study (non-response rate 24.4%). Of the remaining 102 subjects, five were found to be ‘false’ centenarians, eight died after giving their consent but prior to the second visit, and six centenarians or their caregivers did not agree to undergo a second medical visit. The final study group consisted of 83 centenarians (71 women, 12 men) aged 100-107 (mean age 101.1, SD ± 2.1).

Sixty five participants (78.3%) lived with their families, four (4.8%) in nursing homes and 14 (16.8%) lived on their own with assistance of visiting caregivers. Forty five (54.2%) centenarians had primary education (≤ 6 years), including 38 women and 7 men, 27 (32.5%) had secondary education, including 23 women and four men, 11 (13.3%) participants had either complete or incomplete higher education, including 10 women and one man. 33 centenarians suffered from severe visual impairment, 18 from severe hearing impairment and six from both of the above disabilities.

Preliminary assessment of cognitive impairment included the Mini-Mental State Examination (MMSE) (10), and the Six Item Cognitive Impairment Test (6 CIT) (11) from the Blessed Dementia Scale. This test was chosen since, unlike the MMSE, it is entirely verbal and visual impairment does not affect performance. In screening tests, no cutoff point for the whole group was marked that would indicate cognitive impairment, and each case was analyzed individually. The reasons for that included primarily the fact, that there are no cognitive norms available for this age group, and, secondly, that there are no education norms in Poland. Furthermore, a number of factors in centenarians (sight or hearing impairment or motor handicap) may have impact on the number of points scored. The severity of cognitive impairment was classified using the Global Deterioration Scale (GDS) (12), where a score GDS 1 and 2 equals no dementia, GDS 3 – mild cognitive impairment without dementia, and GDS 4, 5, 6, 7 indicate mild, moderate, severe and terminal stage of dementia, respectively. Along with the GDS, the Brief Cognitive Rating Scale (BCRS) (13) was administered to help assess stages of cognitive function. The BCRS tests concentration, recent memory, past memory, orientation, functioning and self-care. The final interpretation of the individual’s cognitive status was based not only on testing data but also included information obtained from caregivers, nursing home records and clinical observation. The Geriatric Depression Scale (14) was used to assess depression. Dementia was clinically diagnosed according to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (15).

Clinical diagnosis of Alzheimer’s disease was determined according to National Institute of Neurological and Communicative Disorders and Stroke – Alzheimer’s disease and Related Disorders Association (NINCS/ADRDA) criteria (16), and diagnosis of vascular dementia according to the 10th Edition of the International Classification of Diseases (ICD 10) criteria (17). The Hachinski scale (18) was applied for calculating an ischemic score to evaluate the risk of vascular dementia. Since for ethical and practical reasons (i.e. transportation problems) the CT examination was not feasible, all diagnoses were considered possible.

The Fisher exact test was used to test differences between the demented and non-demented group with reference to the parameters under examination. P-value < 0.05 was considered to be statistically significant.