Low plasma tryptophan is associated with olfactory function in healthy elderly community dwellers in Japan

Abstract Background Decreased circulating tryptophan (Trp) levels are frequently observed in elderly patients with neurodegenerative disease including Alzheimer’s disease. Trp may serve as a potential biomarker for monitoring disease risk in elderly people. We aimed to investigate the association between low plasma Trp levels and olfactory function, which is known to predict age-related diseases including dementia in elderly people. Methods A total of 144 healthy elderly Japanese community (≥ 65 years old) dwellers from the Health, Aging and Nutritional Improvement study (HANI study) were the subjects of our analysis. Low Trp levels were classified using the lower limit values of the reference interval according to a previous report. Olfactory function was assessed using a card-type test called Open Essence, which includes 12 odour items that are familiar to Japanese people. The elderly subjects with low circulating Trp levels were compared to a control group with normal plasma Trp levels. Results We conducted the analyses using 144 people aged 65 years or older (mean age 73.7 ± 5.5 years; 36.1% men). The subjects showed normal serum albumin levels (4.4 ± 0.2 g/dL) and no daily living disabilities. Low plasma Trp levels (low Trp group) were found in 11.1% of the study population. The low Trp group showed a significantly lower correct-answer rate for the items india ink, perfume, curry and sweaty smelling socks than control group (P < 0.05). There was also a significant association between low Trp levels and low olfactory ability, after adjusting for age and sex. Conclusions Lower plasma Trp levels were associated with a decrease in olfactory function in functionally competent older individuals. Because olfactory dysfunction predicts age-related diseases, low plasma Trp levels may represent a clinical sign of disease risk in elderly people

Plasma Amino Acid Profile in Severely Frail Elderly Patients in Japan

Summary: Background: Severe frailty, which is the highest level of frailty, leads to multiple health impairments that may individually affect the plasma-free amino acid (PFAA) profile. However, the PFAA profile of severely frail patients has not been clarified. The aim of this study was to describe the PFAA profile of severely frail elderly patients. Methods: Elderly patients (aged ≥65 years) who were admitted to the Nukada Institute for Medical and Biological Research (Chiba, Japan) were included. Severe frailty was defined using the Canadian Study of Health and Aging Clinical Frailty Scale. Subjects were divided into non-frail and severely frail groups. The PFAA profile and clinical characteristics of the subjects were analyzed. Results: Compared to the non-frail group (n = 31), the severely frail group (n = 28) had lower body mass index (BMI), serum albumin, serum prealbumin, hemoglobin, and blood pressure and higher C-reactive protein. Seventy-nine percent of severely frail patients had cognitive impairment. Severely frail patients had significantly lower essential amino acid (EAA) plasma concentrations than non-frail patients. Multiple linear regression analysis identified that valine (p = 0.005) was strongly associated with BMI. Valine (p = 0.004), leucine (p = 0.004), tryptophan (p = 0.006), lysine (p < 0.001), and total EAA (p < 0.001) levels were significantly associated with serum prealbumin levels. Conclusion: Severely frail patients had multiple health impairments. BMI and nutritional status were most significantly associated with low EAA levels. Keywords: body mass index, elderly, frailty, nutritional status, prealbumi

Additional file 3: Table S3. of Low plasma tryptophan is associated with olfactory function in healthy elderly community dwellers in Japan

Concentrations of the rate of elderly subjects with low essential amino acid levels and plasma essential amino acid levels in the study population. (DOCX 14 kb

Additional file 1: Table S1. of Low plasma tryptophan is associated with olfactory function in healthy elderly community dwellers in Japan

Concentrations of the rate of elderly subjects with low essential amino acid levels and plasma essential amino acid levels in the study. (DOCX 16 kb

Additional file 2: Table S2. of Low plasma tryptophan is associated with olfactory function in healthy elderly community dwellers in Japan

The concentrations of plasma amino acid and related metabolites of the normal Trp group and the low Trp group. (DOCX 20 kb