THYROID-HORMONE STATUS AND NUTRIENT INTAKE IN THE FREE-LIVING ELDERLY - INTEREST OF REVERSE TRIIODOTHYRONINE ASSESSMENT

Fasting or hypocaloric diets are established methods of inducing low triiodothyronine (T-3) levels that resemble the sick euthyroid syndrome in adults, but little is known on the mechanisms of this syndrome in the elderly. Decreasing T-3 does not seem to be an unavoidable consequence of ageing, but the role of illness or other factors in this decline remains unclear. The aim of this work was to study the influence of nutritional factors on thyroid hormone levels in free-living elderly subjects. A 3-day dietary survey was conducted in 440 randomized subjects aged between 65 and 96. Cholesterol, apoproteins, prealbumin, hemoglobin, thyrotropin-free thyroxine (FT4), FT3 and reverse T-3 (rT(3)) were assayed in each subject. Only 11 subjects had low FT3 levels, and they also had low levels of cholesterol, prealbumin and hemoglobin and a lower Folstein score compared to the rest of the population. Twenty-one subjects had isolated elevated rT(3) levels, they were older and had significantly lower energy and fat intakes than the rest of the population. There was a clear reduction in FT3 levels and an increase in rT(3) levels with age, although in the normal ranges, which occurred despite maintenance of a high-energy intake even in the oldest group. The FT3 level was lower in the subjects with poor health status, whereas high rT(3) levels were associated with low energy intake in men. Stepwise regression showed that hemoglobin, age and prealbumin were the best predictors of FT3 levels, whereas age and energy intake were the main predictors of rT(3) levels. Our results confirm the low prevalence of the low T-3 syndrome in healthy elderly persons, and demonstrate the existence of another group of elderly subjects with isolated elevated rT(3) levels. Whereas a low FT3 level seems to be associated with illness, rT(3) is clearly associated with a low energy intake. Other studies are necessary to appreciate the specificity of this association and the usefulness of rT(3) as an indication of nutrient intake.