Abstract: Effect of age, sex and seasons on the concentration of thyroid hormones (T3 and T4) and thyroid stimulating hormone (TSH) was studied in 25237 thyroid patients who were referred to the radioimmunoassay (RIA) laboratory of the Institute of Radiotherapy and Nuclear Medicine (IRNUM), Peshawar during 1984-1990 (except 1987) and 1995-1996. T3 and T4 of all of these patients were determined by RIA and TSH was determined by immuno-radiometric assay (IRMA). The difference in mean concentration of T3, T4 and TSH in infants and children was non-significant at p<0.05. Comparing all age groups together, higher mean concentration of T3 was found in old age group followed by infants, adults and children. Similarly, the mean concentration of T4 was higher in old age group followed by adults, infants and children. While higher mean values for TSH were observed in infants followed by children, adult and old age group. The infants and children were having significantly higher values of TSH than the old age group and adults at p< 0.05. Concentration of T3 and T4 was significantly higher (p<0.05) in females than males, while TSH concentration was not significantly different (P>0.05) in both sexes. Mean concentration of T3 in summer and autumn was significantly higher than the other seasons and mean concentration of T4 in winter and summer was higher. The mean concentration of TSH in spring and autumn was significantly higher than the mean concentration of TSH in winter and summer at p<0.05.
Introduction
Thyroid hormones namely triiodothyronine (T3), thyroxin (T4) and thyroid stimulating hormone (TSH) stimulate enzymes that are involved in glucose oxidation. These hormones increase the basal metabolic rate and body heat production. Extreme excess of thyroid secretion can cause the basal metabolic rate to rise 60-100% above normal. Complete lack of thyroid secretion usually cause the basal metabolic rate to fall 40-50% below normal (Guyton and Hall, 1996). These hormones also promote growth and development of the brain during fetal life and in the first few years of postnatal life (Elaine and Maieb, 1990). T3 and T4 are synthesized in the thyroid gland and the gland needs iodine for the synthesis of T3 and T4. The requirements of iodine depends on growth, body weight, age, sex and nutritional status of the individual. Climate and disease conditions also affect the requirement of iodine (WHO, 1993).
Age has an effect on the concentration of T3, T4 and TSH. Miller and Block (1970) reported that an increased frequencies of thyroid problems with age. They suggested that gradual increase in autonomous tissue with age was making individual more susceptible to thyroid problems. Lavard (1994) also reported that thyroid problems were less prevalent in infants and children and were increased with age. ICCIDD (1997) reported higher frequencies of thyroid problems in people whose age ware above 40 years.
Sex has also an effect on the concentration of T3, T4 and TSH. Stephen (1992) reported that Asian women had more economic and domestic responsibilities than men. Poor and illiterate women, and their children were more prone to nutritional problems such as goiter, anemia and other disorders. Lavard (1994) reported greater frequency of thyroid problems in females than males. Higher values of thyroid hormones in females in early life, however, with increasing age, the concentration of these hormones dropped in both sexes. The drop was more in females, thus resulting in higher concentration of these hormones in males in old age (Razzak, 1992)
The effect of season on the concentration of T3, T4 and TSH is not very much documented. Tuckova et al. (1995) investigated seasonal fluctuations of thyroid hormones in dogs and observed higher levels of serum T3 and T4 in autumn and winter than in spring and summer. The lowest levels of thyroid hormones were observed in summer in healthy as well as hypothyroid dogs. Riggs (1980) also reported high levels of thyroid hormones in animals during winter. Therefore, the research work was conducted to investigate the effect of age, sex and season on the concentration of T3, T4 and TSH.
Materials and Methods
Size and Location of Sample: 25237 patients visited the RIA laboratory of
the IRNUM, Peshawar for T3, T4 and TSH tests during the
years 1984-1990 (except 1987), 1995 and 1996. Out of these 25237 patients, age
and sex was known for 24522 and 25087 individuals respectively. Out of 24522
age known individuals, 196 were infants (0-1 year), 2011 were children (>1-13
years), 15694 were adults (>13-40 years) and 6621 were of old age (>40
years). Out of 25087 sex known individuals, 6773 were males and 18314 were females.
Out of the total 25237 patients, 7218, 6208, 7798 and 4013 individuals were
referred to the laboratory in winter, spring, summer and autumn, respectively.
Collection of Blood Sample: Blood samples were collected from the patients through a disposable syringes of suitable volume. The samples were transferred into properly labeled sterilized test tubes and were left for 30-60 minutes at room temperature for coagulation. The coagulated blood samples were centrifuged at 1500-2000 rpm for approximately five minutes. Serum were separated and transferred into sterile plastic tubes that were appropriately labeled for the required test, and the date of sample collection. The samples were analyzed either on the same working day or stored at 20oC until analyzed.
Determination of T3, T4 and TSH: T3 and T4 were determined by RIA and TSH was determined by IRMA. Concentrations of T3, T4 and TSH in the serum were measured by using AMERSHAM, RIA and IRMA kits for each hormone. All the kits were provided with standards, tracer antibody in case of T3 and T4, and antibody coated tubes in case of TSH. Assay tubes were labeled as standards, non-specific binding (NSB), total count, patient samples and quality control in duplicate. Procedures recommended by the manufacturer for sample dispensing, incubation and decanting were adopted (Ortho-clinical Diagnostics Amersham, UK, 1998). Gamma Counter (Oakfield instrument LTD, UK, 1995) was used for counting the assay tubes. Hormones concentration were measured by using a computer program (RIASTAT software package).
Statistical Analysis: The data was statistically analyzed with correlation analysis and general linear model procedures by using available SAS statistics package (SAS, 1990).
Results
All individuals, who were referred to the RIA laboratory for T3, T4 and TSH tests, were considered thyroid patients, however, some of them might be normal individuals. This fact was revealed in the actual determination of these hormones where many of the individuals were having normal T3, T4 and TSH levels. The concentration of T3, T4 and TSH levels of different age groups is shown in Table 1. The data revealed that the difference for means T3, T4 and TSH between infants and children was non significant at p<0.05. However, these hormones were significantly different in the adult and old age groups at p<0.05. When compared all age groups together, higher mean values of T3 and T4 were found in old age group. However, these values were in the normal ranges. Higher mean value of TSH were found in infants followed by children, old age and adult groups. The mean values for TSH in infants and children were higher than normal values.
| Table 1: | Effect of age on T3, T4 (nmol L-1) and TSH (miu L-1) levels in thyroid patients |
| Means followed by different letters are significantly different at p<0.05 as determined by t-test. | |
| Table 2: | Effect of sex on T3, T4 (nmol L-1) and TSH (miu L-1) levels in thyroid patients |
| Means followed by different letters are significantly different at p<0.05 | |
| Table 3: | Effect of seasons on T3, T4 (nmol L-1) and TSH (miu L-1) levels in thyroid patients |
| Means followed by different letters are significantly different at p<0.05 | |
The normal ranges for T3, T4 and TSH are 0.8-2.7nmol L-1, 62-165nmol L-1 and 0.5-5.0miu L-1 respectively (Ortho-Clinical Diagnostics Amersham, UK, 1998).
The effect of sex on T3, T4 and TSH levels is presented in Table 2. The T3, T4 and TSH levels in both males and females were in the normal range. Concentration of T3 and T4 was significantly higher in females than males, while TSH concentration was not significantly different (P < 0.05) in both sexes.
The effect of seasons on the concentration of T3, T4 and TSH is given in Table 3. The data indicated that the mean concentration of T3 in summer and autumn was significantly higher as compared to winter and spring at P<0.05. Similarly the mean concentration of T4 in winter and summer was significantly higher than in spring and autumn. But the TSH concentration in spring and autumn was higher than the mean concentration of TSH in winter and summer.
Discussion
The mean concentration of T3, T4 and TSH in all age groups is given in Table 1. The data indicated that T3 and T4 in all age groups were in the normal range. The normal ranges for T3 and T4 are 0.8-2.7 and 62-165 nmol L-1, respectively (Ortho-Clinical Diagnostics Amersham, UK, 1998). However, this normal range was not indicating that all the referred individuals were having normal T3 and T4 values. The reason is that these individuals were referred by qualified doctors and physicians, so majority of them would have thyroid problems. Some of them could be normal individuals and might be referred by doctors and physicians mistakenly. The normal T3 and T4 values in this study were because of the mean values of T3 and T4 for all the patients. The extreme values of T3 and T4 in the data both at lower and higher ends squeezed the mean values of T3 and T4 to normal ranges.
Comparing all age groups together, the mean concentration of T3 and T4 in infants, children, adults and old age were 2.18 and 96.69, 1.94 and 94.98, 2.12 and 104.70 and 2.2 and 107.73, respectively (Table 1). The concentration of both T3 and T4 was significantly higher in old age group than the other age groups and this showed that with increasing age, T3 and T4 were increased. This is due to the increased requirements of these hormones for the various biochemical and physiological functions of the body. Pathological conditions of the individuals may also be a reason for the higher concentration of these hormones in old age. Razzak (1992) found higher concentration of T3 in the age of 40 years and T4 in the age of 60 years. Variation in the concentration of T3 with age has been reported by Riggs (1980).
The mean concentration of TSH in infants and children was 7.22 and 6.51 miu L-1 respectively (Table 1). These values were higher than the normal range of TSH. The normal range of TSH is 0.5-5.0 miu L-1. The higher concentration of TSH than normal may be due to the reason that, in Pakistan, infants and children are usually more prone to hypothyroidism (Malik, 1993 and Zafar, 1994) and this might have lead to higher quantities of circulating TSH. Also during rapid growth period, infants and children usually develop hypothyroidism due to iodine deficiency and in such situations, TSH level is increased (Stanbury and Hetzel, 1980). Razzak (1992) reported higher frequencies of hypothyroidism in infants and children. The concentration of TSH in adults and old age was in the normal range.
The mean concentration of T3, T4 and TSH in males and females are presented in Table 2. The data indicated that both males and females were having normal values of T3, T4 and TSH. Thyroid hormones and TSH levels in both sexes were in the normal range, not because they were all normal individuals but because of the mean values of large number of individuals, where the abnormal values were squeezed to normal values. Concentration of T3 and T4 was significantly higher (p<0.05) in females than males, this provide a clue that females will develop thyroid problems easily. Higher frequencies of thyroid problems in females may be attributed to stress, multiple pregnancies and lactation. Due to particular family set up in Pakistan, females are more exposed to nutritional deficiencies that cause health problems including thyroid disorders. However, with increasing age, the concentrations of these hormones dropped in both sexes. The drop was more in females than males and thus resulting in higher concentration of these hormones in males. The findings of this work apparently contradict the findings of Razzak (1992), however, in the this study, the mean values of T3 and T4 were for males and females of all age groups while Razzak (1992) reported values of T3 and T4 for a particular age group. The higher TSH values in males than females are in fair agreement with the general pattern of T3, T4 and TSH.
The effect of seasons on the concentration of T3, T4 and TSH is given in Table 3. There is a general pattern of increase and decrease in thyroid hormones and TSH. According to that pattern, when thyroid hormones are less, then TSH hormone is high and vice versa This pattern was observed in T4 and TSH, but not in T3 and TSH (Table 3). However, the effect of season on the concentration of thyroid hormones in human subjects has not been established yet.
This investigation concluded that concentration of T3, T4 and TSH are changing with age and T3, T4 concentration are more in females than males. Seasonal variations in the concentration of T3, T4 and TSH are possible.
Acknowledgment
We are thankful to Dr. Sher Muhammad Khan, Director IRNUM, Peshawar for permission to compile the data.