Jordana M. et al.
EQOL (2009) 28-32
THE INFLUENCE OF TOTAL PHYSICAL INACTIVITY
ON PLASMA HOMOCYSTEINE LEVELS. RISK
FACTOR FOR DEVELOPMENT OF
CARDIOVASCULAR DISEASE
Mihaela Jurdana*, Nadja Plazar*, and Rado Pišot**
* College of Health Care Izola, Izola, University of Primorska, Slovenia
** Insitute of Kinesiology research, Science and research centre Koper, University of Primorska,
Slovenia
Abstract
Physical inactivity is the second most significant risk factor for chronic non-infectious contagious
diseases in developed countries. However, conditions have slightly improved in the past few years;
still, only
20 % of the population is being active in a fashion to reduce the probability of
cardiovascular complications. Epidemiological research has confirmed that regular physical activity
and nutrition containing sufficient quantities of folic acid, vitamins B6 and B12, reduce the level of
homocysteine in blood. In our research, we studied the influence of long-lasting inactivity on the level
of homocysteine and folic acid levels in blood. Ten male subjects were resting in horizontal position
for 35 days in a clinical setting. After 35 days of resting we documented a statistically relevant
increase in homocysteine level and decrease of folic acid concentration, despite supervised nutrition.
We can conclude that prolonged physical inactivity is an autonomous, independent risk factor for the
development of cardiovascular diseases.
Keywords: microgravity, physical inactivity, homocysteine, folic acid.
Introduction
Physical activity plays an important role in our lives since it is the cheapest way of strengthening our
health. Of equal importance is the cognition that physical activity reduces the risk factor for the
development of cardiovascular diseases which occupy the leading position.
Scientists agree that regular physical activity prevents the development of obesity, the loss of
muscular mass, insulin resistance, and cardiovascular diseases in sedentary healthy people as well as
in chronic disease patients (Biolo et al., 2005). Homocysteine, an amino acid in blood, which is
produced during the assimilation of methionine, constitutes a risk for the development of
cardiovascular diseases (Nygard et al., 1995; Shai et al., 2004). The level of homocysteine in blood is
strongly influenced by habits such as nutrition, stress, alcohol, or physical inactivity (Stegnar, 2002;
Van Guldener & Stehouwer, 2003; Boden-Albala & Sacco, 2000). Nutrition and alimental substances,
such as folic acid, vitamins B6 and B12, which cooperate as co-enzymes during the assimilation of
homocysteine, are of major importance. Several studies have confirmed that higher levels of group B
vitamins are at least partly connected with lower homocysteine concentrations. Other recent proofs
show that the lowest concentrations of folic acid in blood are connected with the increased risk for a
severe coronary artery disease and stroke. Likewise, it is proved that physical activity reduces the
concentration of total plasma homocysteine and the probability of cardiovascular diseases in healthy
and sick people (El-Khairy et al., 1999; De Bree et al., 2001).
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According to WHO 1.9 million people (600,000 Europeans) die annually due to inadequate
physical activity. This probability increases by 50% among the physically inactive (Kraševec-Ravnik
& Bevc-Stankovič, 2008).
It has been confirmed that physical activity decreases the concentrations of total plasma
homocysteine and thus the probability of developing a cardiovascular disease in healthy and already
sick people (Gaume et al., 2005). There were 620 persons questioned about their weekly physical
activity and lifestyle and levels of their homocysteine concentration measured for the purpose of a
study. The results show that physical activity is an independent lifestyle factor, linked to decreased
concentrations of homocysteine in blood (Dankner et al., 2007).
In regard to the role and importance of physical activity in prevention from cardiovascular
diseases we took part in the research “The influence of simulated weightlessness upon the human
organism” in order to ascertain the connection between prolonged physical inactivity, homocysteine
concentration, and folic acid in blood. We were interested into finding out whether physical inactivity
is an independent risk factor for development of cardiovascular disease.
Methods
Participants and bed rest
Participants
The influence of simulated weightlessness on the human organism was studied as Bed rest
(BR) in research participants who rested in horizontal position for 35 days. Among all registered
volunteers there were ten examinees with no history of neuromuscular or cardiovascular disorders (age
24.3 § 2.6 years) selected on the bases of the following criteria: non-smokers, non-alcoholics, male,
defined age between 20 and 30, personal interview, and medical check. Participants were included in
the research after passing preliminary medical tests and signing their consent. They were informed in
detail about the procedures and risks. The project was carried out in July and August 2007 at the
Valdoltra Orthopaedic Hospital Slovenia, which offered its nursing and technical support. Participants
carried out all their daily activities in horizontal position. Physical activity was strongly forbidden
during all the research period of 35 days. There was passive limb motion and massage lead by a
physiotherapist organized three times a week. With the aim to maintain the body weight the diet was
individually dimensioned taking into consideration healthy eating principles. When the research
started the participants’ basal metabolism was considered in calculating the diet’s compositional and
quantitative balance. During the study the calculations were repeated at weekly intervals to maintain
body weight and fat mass unchanged. The ingredients and the quantity of meals were balanced;
participants had to consume entire meals with no additional intake.
All the participants’ activities were video-monitored 24 hours a day. The study was approved
by the Slovenian National Medical Ethics Committee and was performed in accordance with the
ethical standards laid down in the 1964 Declaration of Helsinki.
Body weight and height
In order to prevent the loss of body mass we provided for regular and individual meals three
times a day and followed the participants’ daily consumption. Body weight (BW in kg) and height
(BH in cm) were measured with the use of common measuring instruments. In addition the body mass
index (BMI in kg/m-2) was also monitored. Body height was measured before and after the research,
while the body weight was registered every week.
Taking blood samples
We took blood samples from the participants before and after the bed rest study. Venous blood
was taken on an empty stomach in the morning (between 7.00 and 7.30 a.m.) into 4 ml vacuum test
tubes
(Beckton-Dickinson, Rutherford, USA). We measured the concentration of total plasma
homocysteine and the concentration of folic acid.
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Statistics
All data are expressed as the mean ± SD with n being the number of participants. Statistical
significance was assessed using the SPSS 15.0 with Student’s paired t-test.
Results
Body height and body weight
The body height did not change statistically during the bed rest research, while the body weight started to
decrease after the third week (BR3) till the fifth week of rest (BR5). The loss of body weight in the third
week (BR3) amounted to 1.6 %, (P<0.001) and in the fifth week (BR5) to 3 %, (P<0.001).
Homocysteine and folate levels
The values of total homocysteine and folates were compared before the bed rest study (BR0) and
during the last, fifth week, right before the getting up (BR5). The research has showed statistically
characteristic changes in the concentration of homocysteine which amounted to 11.19 ± 2.19 µmol/L
before the study, and 12.28 ± 2.96 µmol/L after it, (p=0.014), n= 10; graph 1. Likewise, the concentration
of folates in blood characteristically decreased during the research, from 9.46 ± 3.06 µmol/L to 7.28 ±
1.80 µmol/L, (p=0.007), n= 10; graph 2.
Graph 1
Graph 2
18
18
16
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
before bed rest (BR0)
after bed rest (BR5)
before bed rest (BR0)
after bed rest (BR5)
Graph 1: Plasma folate concentration in participants’ blood before the bed rest study (BR0) and in the
fifth week (BR5) of bed rest. The concentration statistically characteristically decreases in the fifth week
(p= 0.007).
Graph 2: Plasma homocysteine concentration in the participants’ blood before the bed rest study (BR0)
and in the fifth week (BR5) of bed rest. In the last blood sample taking during the fifth week of bed rest
(BR 5), the concentration of homocysteine statistically typically increased (p=0.014).
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Discussion
All ten volunteers participating in the research successfully passed a 35-day horizontal bed rest as well as
a couple of weeks of rehabilitation. Since the participants’ diet was managed individually in order to
assure a neutral energetic balance, the participants had to consume entire meals with no additional intake.
As the calorie intake was calculated on the bases of weekly measurements of participants’ weight a major
loss of weight was prevented, and gaining of excessive fat mass suppressed. Despite the fact that the
nutrition was monitored with controlled intake of singular ingredients and micronutrients, folic acids
being among them, the folic acid decreased significantly after the five-week bed rest, yet within the
reference value range. A moderate homocysteinemia was also recorded after five weeks, the level of
dangerous homocysteine increased significantly, exceeding the reference values. The latter demonstrates
the inverse ratio between folic acid and homocysteine concentration, already confirmed by previous
studies (Siri et al., 1998). Increased homocysteine is presumably responsible for at least a 10 % risk for
the development of atherotrombotic vascular disease
(Clarke et al.,
2001), and a moderate
homocysteinemia is nearly as important risk factor for development of atherotrombosis as smoking and
hyperlipidemia (Chen et al., 1999).
The “Bed rest” or “The influence of simulated weightlessness upon the human organism” is an
international research of interdisciplinary nature involving numerous foreign and domestic scientists. Its
objective is to study the influence of inactivity upon the human body, and above all, the effect of
simulated weightlessness on skeleton-muscular, thermo-regulatory, as well as cardiovascular system.
Such studies are important not just for the space flights’ preparation but also for the investigation of
consequences of prolonged bed rest after a surgery. It is thus at this point that interests of “spatial” and
“terrestrial” medicine intersect.
Along with the building of the international space station Freedom human presence in space has
been steadily increasing. Until now, astronauts have spent a year at the most in space. On the basis of
such space experience as well as terrestrial experiments, we have become aware of the fact that a non-
gravity condition causes certain changes which can be harmful after a long stay in space. The ongoing
terrestrial researches are aimed at the comprehension of the causes of these changes and at the
development of precautions which could prevent harmful physiological changes. In our research, we have
followed and tried to determine in what way long-lasting rest or inactivity affects the level of
homocysteine in blood and to establish the linkage between the level of homocysteine and folates in
nutrition. The results of the research will be useful not only for space workers of future but also for the
comprehension of physiological changes among immobilized patients.
Horizontal bed rest
(BR) or microgravity is one of the most frequently used methods of
monitoring the consequences of total physical inactivity (Adams et al., 2003; Eiken and Mekjavić, 2002).
Since several studies indicate physical activity as an independent lifestyle factor connected with lower
homocysteine concentration (Danker et al., 2007), our research could confirm that physical inactivity is
an independent risk factor for the development of cardiovascular diseases, although we cannot state with
accuracy that after five weeks the level of dangerous homocysteine increased above the critical level due
to physical inactivity or folic acid decrease.
Conclusion
Our research findings confirmed the importance of exercise and physical activity in the prevention of
cardiovascular diseases. It has been evidenced that prolonged rest increases the levels of homocysteine in
blood, negatively influencing the cardiovascular system. The latter makes it clear that the same
consequences can result from prolonged physical inactivity in everyday life.
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Reference
1. Biolo G, Ciocchi B, Stulle M, Piccoli A, Lorenzon S, Dal Mas V, Barazzoni R, Zanetti M and
Guarnieri G (2005). Metabolic consequence of physical inactivity. J Ren Nutr 2005, 15(1), 49-53.
2. Nygard O,Vollset SE, Refsum H, Stensvold I, Tverdal A, Nordrehaug JE, Ueland M and Kvåle G
(1995). Total plasma homocysteine and cardiovascular risk profile. The Hordaland Homocysteine
Study. JAMA, 274(19), 1526-1533.
3. Shai I, Stampfer MJ, Ma J, Manson JE, Hankinson SE, Cannuscio C, Selhub J, Curhan G and Rimm
EB (2004). Homocysteine as a risk factor for coronary heart diseases and its association with
inflammatory biomarkers, lipids and dietary factors. Atherosclerosis, 177(2), 375-381.
4. Stegnar M (2002). Hiperhomocisteinemija in žilna bolezen. Farm Vestn, 343-346.
5. Van Guldener C and Stehouwer C (2003). Homocysteine metabolism in renal disease. Clin Chem Lab
Med, (41), 1412-1417.
6. Boden-Albala B and Sacco RL (2000). Lifestyle factors and stroke risk: Exercise, alcohol, diet,
obestity, smoking, drug use and stress. Curr Atheroscler Rep, 2(2), 160-166.
7. Siri PW, Verhoef P and Kok FJ (1998). Vitamins B6, B12, and folate: association with plasma total
homocysteine and risk for coronary atherosclerosis. J Am Coll Nutr, 17(5), 435-441.
8. Kraševec-Ravnik E and Bevc-Stankovič M. Svetovni dan gibanja 2008: Telesna dejavnost za vse.
(2008): http://www.ivz.si/index.php?akcija=novica&n=1528.
9. Gaume V, Mougin F, Figard H, Simon-Rigaud ML, N'Guyen UN, Callier J, Kantelip JP and
Berthelot A (2005). Physical training decreases total plasma homocysteine and cysteine in middle-
aged subjects. Ann Nutr Metab, 49(2), 125-31.
10. Dankner R, Chetrit A, Dror GK et al. (2007). Physical activity is inversely associated with total
homocysteine levels, independent of C677T MTHFR genotype and plasma B vitamins. Age,
(29),
219-227.
11. Clarke R, Levington S, Donald A, Johnston C, Refsum H, Stratton I, Jacques P, Breteler MM and
Holman R (2001). Understiation of the importance of homocysteine as a risk factor for cardiovascular
disease in epidemiological studies. J Cardiovasc Risc, 8, 396-399.
12. Chen P, Poddar R, Tipa EV, Dibello PM, Moravec CD, Robinson K, Green R, Kruger WD, Garrow
TA and Jacobsen DW (1999). Homocysteine metabolism in cardiovascular cells and tissues:
implications for hyperhomocysteinemia and cardiovascular disease. Adv Enzyme Regul, 39, 93-109.
13. Eiken O and Mekjavic IB (2002). The Valdoltra Bedrest Study: Effects of 35 days of
horizontal bedrest on the unction of peripheral blood vessels, the thermoregulatory system
and on the function and structure of the musculoskeletal system. Report No. FOI-R-0748-SE.
Swedish Defence Research Agency (FOI), NBC Defence, Defence Medicine: Umea. (2002).
14. Adams GR, Caiozzo VJ and Baldwin KM (2003). Skeletal muscle unweighting: spaceflight and
ground-based models. J Appl Physiol, 95(6), 2185-2201.
32