Body Weight Changes Clinical Trial
Official title:
The Effect of Potassium Bicarbonate on Bone and the Immune System During 21 Days of 6° Head- Down- Tilt Bedrest (HDT- Bedrest)
Mainly due to the absence of gravitational forces in weightlessness, astronauts suffer from
an increased bone loss- negatively affecting health and vitality during a mission. The
development of effective countermeasures to this loss includes many different aspects like
sports but also nutrition.
Alkaline salts, abundant in fruits and vegetables, have shown to have positive effects on
markers of bone turnover of postmenopausal women but also men and younger adults. With the
current study the effects of a potassium bicarbonate supplementation added to a
standardised, strictly controlled, definite diet of healthy, young men, should be verified
within 21 days of 6°- HDT- Bedrest- the gold standard of simulating weightlessness within
earthbound conditions.
Astronauts in space suffer from an increased bone loss which is mainly related to the
absence of gravitational forces. This increased bone reduction is accompanied by an higher
concentration of calcium in urine and in this respect enhancing the risk of renal stones.
Due to the fact, that bones´ regeneration does not occur rapidly even after returning to
earth, astronauts face an increased risk of osteoporosis.
Nutritional factors such as a deficient intake of calcium, energy and fluid and the abundant
intake of table salt exhibit additional negative effects on bone. Results of several studies
consistently show the negative effects of acids on bone (increased bone loss). With respect
to space missions of longer duration one big challenge is the development of countermeasures
for the negative consequences of weightlessness on bone.
As not all needed experiments for the development of countermeasures can be conducted in
space, simulation models of weightlessness such as 6° Head- Down- Tilt- Bedrest (HDT-
Bedrest) have been implemented on earth, miming some physiological conditions of
weightlessness such as unloading and immobilisation of the lower parts of the body and the
fluid shift.
Alkaline salts, such as potassium bicarbonate (KHCO3), demonstrate positive effects on bone
when being supplemented to postmenopausal women. Apart from the positive effects on markers
of bone turnover, calcium concentration in urine could be reduced. Thus, the main aim of the
present study was to reduce the immobilization induced bone resorption through an alkalizing
effect of the alkaline salt KHCO3`s supplementation during Head- Down- Tilt- Bedrest (HDT-
Bedrest)-a leading simulation model of weightlessness.
The crossover designed study consisted of two parts of equal length (36 days)- 7 days of
adaptation, 21 days of HDT- Bedrest, 6 days recovery and 2 days of long- term follow- up.
Both study parts only differed in the HDT- period, where one group of the 8 healthy, young,
male participating subjects was supplemented with 90 mmol KHCO3 daily (3 times a day 30 mmol
KHCO3 diluted in 200 ml tab water, supplemented together with the main meals), while the
other group only received 200 ml of tab water without any supplementation (Control group).
The measurements of bone formation markers as well as bone resorption markers in blood and
urine supply insight into the influences of the supplementation on bone metabolism while
blood gas analysis together with the pH- values of the 24h- urine point out the alkalising
effects of KHCO3. Further physiological systems like protein and muscle metabolism, body
weight and body composition, circulation and the neuro- vestibular system are simultaneously
under investigation.
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