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Basal metabolic rate and thyroid hormones of late-middle-aged and older human subjects: the ZENITH study
N Meunier1, J H Beattie, D Ciarapica
1Centre de Recherche en Nutrition Humaine d'Auvergne, Unité des Maladies Mé taboliques et Micronutrients, INRA, Clermont-Ferrand/Theix, France.
Objective:
This paper describes baseline data on basal metabolic rate (BMR), thyroid hormone levels and body composition of middle-aged and older people participating in the ZENITH project and the correlation of thyroid hormone levels with zinc status.
Design:
A multicentre prospective intervention study employing a randomised double blind design.
Setting:
Clermont-Ferrand, Theix (France), Coleraine (Northern Ireland), Grenoble (France), Rome (Italy).
Interventions:
BMR has been measured on a subsample of 70 middle-aged volunteers (35 men and 35 women recruited in Clermont-Ferrand, France, aged 55-70 y) and 108 older volunteers (56 men and 52 women recruited in Rome, Italy, aged 70-85 y). Thyroid hormone levels were evaluated in the entire group of ZENITH volunteers (n = 387). BMR was measured by indirect calorimetry. Fat-free mass (FFM) was derived by four skinfold thicknesses using Durnin and Womersley's equations. Concentrations of thyroid hormones (total T3 and T4) were measured using a competitive immunoassay with an enhanced chemiluminescence end point.
Results:
Italian older volunteers had a significantly lower FFM than middle-aged French volunteers (-7% P < 0.01). A negative correlation between BMR and age (men, r = -0.64; women, r = -0.62; both P < 0.0001) was observed: BMR was significantly (P < 0.000001) lower in Italian elderly volunteers (4.03+/-0.46 kJ/min and 3.29+/-0.42 kJ/min for men and women, respectively) than in middle-aged French volunteers (4.84+/-0.45 kJ/min and 3.87+/-0.38 kJ/min for men and women, respectively), even after adjustment for FFM (-12%). No correlation has been observed between BMR and thyroid hormones both in French and Italian subjects. Total T4 (TT4) concentrations were lowest in middle-aged population (-10%, P < 0.0001). A moderate negative correlation has been found with TT4 and red blood cell zinc (r = -0.12, P < 0.02, slope -0.026).
Conclusions:
The results confirm an age-related decline in BMR not entirely explained by body composition or thyroid hormones differences.
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