In this study the investigators aim to investigate whether the sympathetic stimulation of BAT, as assessed with a 123I-metaiodobenzylguanidine single-photon emission computed tomography computed tomography scan, differs between young and elderly subjects, as an explanation for the diminished metabolic brown adipose tissue activity in the elderly.

The investigators hypothesis is that sympathetic nervous system activity in the elderly is diminished as compared to their younger counterparts as an explanation for the diminished metabolic brown adipose tissue activity in the elderly.

The sympathetic nervous system is the primary activator of Brown Adipose Tissue.

Elderly are known to have less metabolically active brown adipose tissue as compared to their younger counterparts.

The reason for this diminished metabolic brown adipose tissue activity is unknown.

However, a lower sympathetic nervous system activation to brown adipose tissue in the elderly might explain a diminished metabolic brown adipose tissue.

Therefore, in this study, both the sympathetic nervous system activation to brown adipose tissue and the metabolic activity will be measured in young and older subjects.

sympathetic nervous system activity will be measured using 123I-metaiodobenzylguanidine single-photon emission computed tomography computed tomography scans, metabolic activity will be measured using 18F- fluorodeoxyglucose positron emission tomography CT scans.

Inclusion Criteria:

• Male
• Caucasian origin
• Subjects should be able and willing to give informed consent
• 18-65 years old
• BMI range of 19-27 kg/m2

Exclusion Criteria:

• Renal failure (creatinine>135mmol/l)
• Daily use of prescription medication
• Prior participation in a research protocol involving radiation exposure in the last 2 years

Healthy Caucasian Males