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Letters |
1
Dept. de Nutricion y Bromatol., Facultad de Farmacia, Universidad de Granada, E-18071 Granada, Spain,
2
Policlínica Granada.
a Author for correspondence.
To the Editor:
Nowadays, there is growing interest in the possible relationship between selenium metabolism and the aging process (1). Epidemiological studies show that selenium may have a preventive role in some degenerative diseases such as hepatic cirrhosis, cardiovascular diseases, and some types of cancer (2)(3). However, information on the influence of selenium on aging is contradictory, apart from the fact that the process is not yet well understood.
We determined the serum concentrations of Se in 93 institutionalized elderly people in Granada (Spain) as a short-term indicator of human selenium status and its correlation with nutrient intake. In addition, taking into account the role of Se in oxidation, in metabolic changes in plasma lipids, and as a component of glutathione peroxidase, we examined other biochemical markers, e.g., total cholesterol, LDL-cholesterol, HDL-cholesterol, and triglycerides. We likewise studied leukocyte numbers in blood, as an indicator of risk of disease through infection, and established their correlation with serum Se concentrations.
To quantify serum selenium, we used the hydride generation atomic absorption spectrometry technique previously optimized (4). Daily dietary intake was determined by the 7-day weighed food record, including a day off (5). Unfortunately, determination of Se intakes was not possible because the software used to calculate the nutritional composition of the foodstuffs did not include Se.
The concentration of serum selenium in the institutionalized elderly
people is shown in Table 1
. No significant differences according to sex were noted.
Depending on the age of the subjects in the two groups considered, the
serum selenium decreased significantly in women (P <0.05)
but not in men (probably because of the low number of men examined in
the study).
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According to Campbell et al. (6), aging per se has very
little effect on the status of selenium; that is, intercurrent illness
and reduction in food intake are the most important factors in the
reduction in the status of this element in old age. In a study
comparing healthy elderly subjects (both institutionalized and
noninstitutionalized) with a group of young adults, no statistically
significant differences between the groups were found in selenium
concentrations in plasma or in glutathione peroxidase activity(1). The same was observed in this study, comparing serum
selenium concentrations in institutionalized elderly subjects in
Granada (Table 1
) with those in younger adult subjects from coastal and
mountain towns of the same province (4) (i.e., 74.9 ±
27.3 µg/L selenium). This result could be explained by the known
influence of geographical origin on selenium concentrations in the food
produced in the area and, ultimately, on the daily dietary intake of
selenium (7); this, in turn, affects the concentrations of
this element in the subjects' serum.
Several studies have found that Se concentrations in plasma(2)(6), and serum (8) of healthy elderly people
were significantly lower than those in young adults. However, other
researchers investigating people of ages >60 years have indicated that
age does not affect the concentration of serum Se (9).
Nonetheless, with regard to the age of the institutionalized elderly
people, the concentration of selenium was significantly lower
(P <0.05) in women older than 80 years. This result may be
related to the highly heterogenic characteristics of the very elderly,
along with a significant decrease in energy intake (from 1850 ±
254 kcal daily in women of <80 years to 1679±234 kcal daily in women
of 
80 years; P <0.01).
We also correlated serum selenium concentrations with macronutrient intake. The only positive correlation (P <0.05) was with the intakes of polyunsaturated fatty acids, both for all samples (r = 0.2627) and for samples from women only (r = 0.3637), as was previously found in serum(10) of healthy subjects. This finding could reflect the known positive influence of polyunsaturated fatty acids on selenium bioavailability (8).
Significant relationships (P <0.05) were observed between the serum selenium concentrations and plasma total cholesterol (r = 0.2965 in all subjects; r = 0.3439 in women) as well as LDL-cholesterol (r = 0.2765 in all subjects; r = 0.3020 in women). The same statistical association between serum selenium and total cholesterol has been previously indicated (11). The present study thus reinforces the important role of Se in prevention of cardiovascular disease(12).
Finally, we also found a statistically significant negative correlation (P <0.05) between serum selenium concentrations in institutionalized elderly subjects and numbers of leukocytes in blood in all the subjects (r = -0.2316) and in women (r = -0.1727). However, we saw no statistical difference for the leukocytes in all subjects by sex or age groups. Therefore, the results obtained in the present study lead us to suggest that this probably reflects the role of Se in leukocyte synthesis and activity, although the mechanism and manner in which Se concentrations regulate blood leukocytes are unclear and require further research. Nevertheless, this result establishes the importance of the conservation of an appropriate selenium status, especially in the elderly, to avoid a reduction of the immunological reaction and an increase of infection-related morbidity associated with aging(13).
We did not observe a clear correlation in the biochemical markers under
consideration (serum selenium, total cholesterol, LDL-cholesterol,
HDL-cholesterol, triglycerides, and leukocytes) between the two age
groups (<80 years; 80 years) and so could establish no relation
between serum Se concentrations and cellular aging in the
institutionalized elderly subjects under consideration. The fact that
most of the experimental studies on influences of Se status in aging
have not been able to decisively determine at what concentration and in
what way the influence is established in the degenerative diseases
associated with old age suggests that more research is needed in this
area.
References
The following articles in journals at HighWire Press have cited this article:
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  J. Bleys, A. Navas-Acien, S. Stranges, A. Menke, E. R Miller III, and E. Guallar Serum selenium and serum lipids in US adults Am. J. Clinical Nutrition, August 1, 2008; 88(2): 416 - 423. [Abstract] [Full Text] [PDF]
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