PTH And Calcium Responses to Exercise (PACE) in Older Adults

Determine whether the magnitude of dermal Ca loss (i.e., sweating) during exercise is a
determinant of the decline in iCa and increases in PTH and carboxy-terminal collagen
crosslinks (CTX; marker of bone resorption). The proposed experiment will address this by
manipulating the rate of dermal Ca loss (moderate vs high sweating rate) to determine whether
this is the trigger for the cascade described in Figure 1. This will be achieved by having
participants perform two identical exercise bouts under different thermal conditions (warm vs
cool).

Inclusion Criteria:

- Healthy adults aged 60-80 y

Exclusion Criteria:

- Use of medications in the past 6 months known to affect bone metabolism (e.g.,
bisphosphonates, thiazide diuretics, oral glucocorticoids)

- BMD t score < -2.5 at the total hip or lumbar spine

- Known disease or condition associated with intestinal malabsorption

- Moderate or severe renal impairment defined as an estimated glomerular filtration rate
of <60 mL/min/1.73m2 based on the MDRD equation

- Chronic hepatobiliary disease, defined as liver function tests (AST, ALT) >1.5 times
the upper limit of normal; if such values are obtained on initial screening and
thought to be transient in nature, repeated testing will be allowed

- Thyroid dysfunction, defined as an ultrasensitive TSH <0.5 or >5.0 mU/L; volunteers
with abnormal TSH values will be re-considered for participation in the study after
follow-up evaluation by the PCP with initiation or adjustment of thyroid hormone
replacement

- Serum calcium <8.5 or >10.3 mg/dL

- Serum 25(OH)D <20 ng/mL; volunteers with abnormal serum 25(OH)D values may be
re-considered for participation in the study if serum 25(OH)D is >20 ng/mL after
vitamin D supplementation

- Uncontrolled hypertension defined as resting systolic BP >150 mmHg or diastolic BP>90
mmHg; participants who do not meet these criteria at first screening will be
re-evaluated, including after follow-up evaluation by the PCP with initiation or
adjustment of anti-hypertensive medications

- History of type 1 or type 2 diabetes

- Cardiovascular disease; subjective or objective indicators of ischemic heart disease
(e.g., angina, ST segment depression) or serious arrhythmias at rest or during the
graded exercise test (GXT) without follow-up evaluation will be cause for exclusion;
follow-up evaluation must include diagnostic testing (e.g., stress echocardiogram or
thallium stress test) with interpretation by a cardiologist

- Diagnosis or history of asthma