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Alex Vermeulen

Publications and source records attributed to Alex Vermeulen.

4 recordsLinked to original sources
PubMed2005

The decline of androgen levels in elderly men and its clinical and therapeutic implications.

Aging in men is accompanied by a progressive, but individually variable decline of serum testosterone production, more than 20% of healthy men over 60 yr of age presenting with serum levels below the range for young men. Albeit the clinical picture of aging in men is reminiscent of that of hypogonadism in young men and decreased testosterone production appears to play a role in part of these clinical changes in at least some elderly men, the clinical relevancy of the age-related decline in sex steroid levels in men has not been unequivocally established. In fact, minimal androgen requirements for elderly men remain poorly defined and are likely to vary between individuals. Consequently, borderline androgen deficiency cannot be reliably diagnosed in the elderly, and strict differentiation between "substitutive" and "pharmacological" androgen administration is not possible. To date, only a few hundred elderly men have received androgen therapy in the setting of a randomized, controlled study, and many of these men were not androgen deficient. Most consistent effects of treatment have been on body composition, but to date there is no evidence-based documentation of clinical benefits of androgen administration to elderly men with normal or moderately low serum testosterone in terms of diminished morbidity or of improved survival or quality of life. Until the long-term risk-benefit ratio for androgen administration to elderly is established in adequately powered trials of longer duration, androgen administration to elderly men should be reserved for the minority of elderly men who have both clear clinical symptoms of hypogonadism and frankly low serum testosterone levels.

Aged↗
PubMed2005

Monitoring and modelling of biosphere/atmosphere exchange of gases and aerosols in Europe.

Monitoring and modelling of deposition of air pollutants is essential to develop and evaluate policies to abate the effects related to air pollution and to determine the losses of pollutants from the atmosphere. Techniques for monitoring wet deposition fluxes are widely applied. A recent intercomparison experiment, however, showed that the uncertainty in wet deposition is relatively high, up to 40%, apart from the fact that most samplers are biased because of a dry deposition contribution. Wet deposition amounts to about 80% of the total deposition in Europe with a range of 10-90% and uncertainty should therefore be decreased. During recent years the monitoring of dry deposition has become possible. Three sites have been operational for 5 years. The data are useful for model development, but also for model evaluation and monitoring of progress in policy. Data show a decline in SO(2) dry deposition, whereas nitrogen deposition remained constant. Furthermore, surface affinities for pollutants changed leading to changes in deposition. Deposition models have been further developed and tested with dry deposition measurements and total deposition measurements on forests as derived from throughfall data. The comparison is reasonable given the measurement uncertainties. Progress in ozone surface exchange modelling and monitoring shows that stomatal uptake can be quantified with reasonable accuracy, but external surface uptake yields highest uncertainty.

Aerosols↗
PubMed2002

Ageing, hormones, body composition, metabolic effects.

The age-associated, progressive changes in body composition are paralleled by a progressive decrease in hormone levels, among which there are testosterone (T) and growth hormone (GH). Moreover, the age-associated changes are rather similar to the changes in body composition seen in hypogonadism or hyposomatotropism, respectively. These age-associated changes in body composition are rather important: a decline in muscle mass by 20%-40% between the ages of 25 and 75, a doubling of fat mass and a decrease in bone mineral density by 0.3% per year after age 35. They have important functional and metabolic consequences. Most studies show a significant positive correlation between muscle mass and bone mineral density, respectively, and plasma T or GH levels, whereas abdominal fat mass is generally negatively correlated with T and GH levels. Whether, however, the hormone levels play a causal role or are the consequence of the changes in body composition is still an unsettled problem. The beneficial effects of hormone substitution on body composition suggest, nevertheless, that T and GH are at least co-determinants of the observed age-associated changes.

Aging↗