This study showed high prevalence of anemia in population aged 65 year and older, regardless of gender. Its prevalence increase significantly with age, and the trend of prevalence also showed considerable increase. Comorbid conditions including underweight, DM, rheumatoid arthritis, cancer, and CRF were shown as significant risk factors.
There are few reports on anemia in older population in Korea. Kim et al., showed that the incidence of anemia in population aged over 60 years in Korea was 7.2%, and most of them were anemia of chronic disease. Han et al., analyzed healthy individuals who underwent routine medical checkup in single center and showed that mild anemia, defined as hemoglobin level between 10.0 g/dL and 12.9 g/dL in men and 10.0 g/dL and 11.9 g/dL in women, is a risk factor for cancer and cardiovascular death in elderly population. Jeong et al., also showed the high incidence of anemia in population aged 80 years and more, and most of them were anemia of unknown reason, which was closely related to malignancy by analyzing routine medical checkup laboratory data. These studies are small community-based cross-sectional study with selected population, and have limitation to reflect general Korean population. This study analyzed the KNHANES data, which was elaborately designed and conducted as government-lead nation-wide survey with carefully sampled participant. Therefore, result of this study surely represent the current status of older population in Korea.
However, result in this study have difficulty in generalizations since populations with laboratory data showed significant different characteristics compared to populations without laboratory data. Whether or not to do laboratory test was left entirely to the participants and the decision was made by family unit in KNHANES, so missing laboratory data group was not randomly distributed. This seems to contribute to the differences.
The occurrence of anemia in older people is not fully understood. Hemoglobin levels in the older population are reportedly lower than the reference values for other population groups. Some reports concluded that this decrease in hemoglobin levels might be one of the consequences of the normal aging process; hence, the criteria for anemia should be different in this population[13, 24-27]. However, many reports also showed that anemia in older persons is related to the presence of underlying health conditions and is therefore associated with high mortality and morbidity. Furthermore, most people with anemia have been shown to have nutritional deficiency, but the etiology is unknown in one-third of anemia cases[17, 28]. This unexplained category of anemia includes aging-related clonal hematopoiesis (ARCH), idiopathic cytopenia of undetermined significance (ICUS), and pre-myelodysplastic syndrome (MDS); these conditions are associated with a low but potential risk of hematologic malignancy[19, 20, 29]. Therefore, older people with anemia are recommended to undergo evaluations for etiology analysis. However, there is no guideline or consensus for the range and frequency of the evaluation and management of this population.
Reports on prevalence of anemia differs according to the studies, and these differences might be attributed to the diversity of the subjects and cohorts of previous studies[4, 17, 23, 24, 27]. Studies conducted in nursing home- and hospital-based populations have shown significantly higher prevalence of anemia and morbidity[3, 10]. Most of these studies seem to show similar findings with regard to the prevalence of anemia in older adults—that is, the prevalence of anemia tends to increase with age, and there is no sex difference, with some studies even showing a higher prevalence of anemia among males. In particular, a study in the U.S. showed that in people aged >85 years, the prevalence of anemia was higher among males.
In this study, the prevalence of anemia in the population aged ≥65 years was 14.0%, which is higher than previous reports, for example, 10.6% in U.S. and 8.33% of Bang et al. Since study settings and participants enrolled are different, it is not reasonable to compare directly. However, this finding is quite striking because this study was based on populations who were relatively healthy and lived in a secure environment. Besides, it is expected that the prevalence of anemia would be much higher in those who live in a less secure environment, are admitted in hospitals or social facilities, and experience malnutrition due to financial reasons. Studies in admitted patients and people with diseases have shown that anemia is associated with a high risk of complications and poor outcomes.
This study showed that older adults with anemia were tends to be underweight, which might be related to malnutrition. However, this finding is inconsistent with those of previous studies showing that being a beneficiary of social allowance or having a low household income is not a risk factor for anemia. Malnutrition-related anemia in elderly has been reported to be 34 ~62% of anemia of known etiology[17, 23, 30, 31]. Most of malnutrition-related anemia consist of iron, folate, and vitamin B12 deficiency. Among them, iron deficiency is the most common, and is usually accompany with other co-morbidities, i.e., GI bleeding, chronic inflammation, and so on. Malnutrition also can be induced by chronic disease-related, i.e., chronic renal failure, or psychologic- related, i.e., depression, anorexia. Moreover, malnutrition also correlates to the economic status or household financial burden[28, 31]. This nationwide survey did not include any other specific data for malnutrition aside from body weight. Further study is thus required to clarify the relationship between anemia and malnutrition.
This study is limited in that the KHNANES data cannot be used to show a causal relationship between variables. To determine the cause-and-effect relationship between these variables, large well-designed prospective cohort studies are necessary. Another limitation is that the questionnaire items of the KHNANES are being revised every 3 years for economic reasons, making it impossible for researchers to investigate the possible etiologies of anemia in the study population. As the etiologies of anemia seem to be more complicated in older adults than in the younger population, anemia may pose a heavy medical burden on older people in countries such as South Korea.