|Blood glucose and insulin
Type 2 diabetes, heart disease, arteriosclerosis,
liver disease, elevated cholesterol and hypertension are among the
medical conditions associated with insulin insensitivity and elevated
blood glucose levels .
Calorie restricted animals show a significantly
increased sensitivity to insulin compared to freely fed animals. CR also
has a significant impact on insulin sensitivity in humans , .
With normal aging, people tend to develop abdominal
obesity. High levels of intra abdominal fat have been found to be
predictive of heart attack risk and also linked to high cholesterol,
high blood pressure, high triglycerides. There is a strong association
between increased waist circumference, insulin insensitivity and type 2
diabetes. Yoga practice seems to weaken this link .
High levels of stress lead to increased cortisol
levels, which is associated with higher levels of abdominal fat. Any
form of exercise would help to reduce visceral fat and thus reduce
It has been suggested that relaxation and stress
reduction may not cause overall weight loss, but may result in a
healthier distribution of body fat . It has been found that there
were favourable metabolic changes in overweight and underactive subjects
who practiced restorative yoga . The effect of restorative yoga on
body fat distribution would make an interesting basis for further study.
A recent study found that long term yoga practice was
associated with increased insulin sensitivity, and significantly lowered
fasting plasma insulin levels .
In a 45 day study on people with Type 2 diabetes, all
patients continued to take conventional medicines. The study group
practiced asana and pranayama, while the control group did not practice
yoga. The yoga group showed significant improvement in blood glucose,
lipid profile and insulin levels and a decrease in BMI (body mass
index). The control group showed an increase in weight, and non
significant improvement in the other parameters .
Reviews of published studies found that yoga
interventions are generally effective in reducing body weight and
glucose levels , , . These studies suggest that yoga can
have a beneficial effect on glucose tolerance and insulin sensitivity.
Blood lipid profile
HDL (high density lipoprotein - good cholesterol)
helps to remove cholesterol from the blood, protecting from
cardiovascular disease. Higher levels of HDL are correlated with better
LDL (low density lipoprotein - bad cholesterol) is
thought to deposit cholesterol in artery walls, increasing the risk of
heart disease. High levels of LDL are associated with atherosclerosis.
This includes VLDL (very low density lipoprotein).
Along with reductions in basal metabolic rate (BMR),
people on CR diets experienced large reductions in LDL cholesterol, and
had very high levels of HDL cholesterol .
In a study on normal, healthy volunteers, after 30
days of practicing pranayama, a significant reduction in triglycerides,
free fatty acids and VLDL cholesterol along with significant elevation
of HDL cholesterol was observed in the men. Free fatty acids were
reduced in women.
After adding asana exercises to the pranayama for
another 60 days, free fatty acids increased in both men and women, and
women demonstrated a significant fall in serum cholesterol,
triglycerides, LDL and VLDL cholesterol .
It is of interest that free fatty acid levels
increased after the subjects started doing asana exercises. It is
possible that their bodies were breaking down fat. Further research
would aid in clarifying this somewhat contradictory effect.
In another study on patients with coronary artery
disease, at the end of one year of yoga training, total cholesterol was
reduced by up to 23% in the yoga group of patients, compared to 4.4% in
the control group. LDL cholesterol was reduced by 26% in study group
patients as compared to 2.6% in the control group. A much higher
proportion of the yoga group showed regression and arrest of progression
of the disease than in the control group .
Studies indicate that pranayama and yoga asanas can
be helpful in patients with lipid metabolism disorders , and have a
positive effect on blood lipid profile, reducing cholesterol , ,
Melatonin is produced by the pineal gland, and
appears to have anti aging properties , likely due to its
antioxidant properties. It is also a natural immune enhancer and has
been shown to extend longevity in some animal studies . Higher
melatonin levels are also associated with an increased sense of well
Melatonin is released mainly at night during sleep.
Moderate physical activity has been shown to increase production of
Calorie restriction has been shown to prevent the
usual age related decline in melatonin levels in monkeys .
Yoga and meditation have been shown to significantly
increase melatonin levels, with regular meditators found to have a
higher level of melatonin than non-meditators , , .
In a 2004 study on normal, healthy volunteers, a yoga
group practiced asana, pranayama and meditation while a control group
did body flexibility exercises, slow running, and played games.
Yogic practices for 3 months resulted in an
improvement in cardiorespiratory performance and psychological profile,
with an improved sense of well being. The maximum night time melatonin
levels in yoga group showed a significant correlation with well-being
The yoga group showed an increase in plasma
melatonin, indicating that yoga could be used as a psychophysiologic
stimulus to increase endogenous secretion of melatonin .
In another study, experienced meditators practising
either TM-Sidhi or another form of yoga showed significantly higher
plasma melatonin levels in the period immediately following meditation
compared with the same period at the same time on control nights. It was
concluded that meditation, at least in the forms studied here, can
affect plasma melatonin levels .
Longer term studies are required to ascertain whether
the higher melatonin levels in yoga practitioners and meditators are
Basal metabolic rate and body temperature
Studies measuring metabolic rate in CR animals
indicate that it lowers the BMR. CR in animals is associated with a
robust decrease in energy metabolism, including a lowering of resting
metabolic rate, lowering of the thermic effect of meals and a decrease
in the energy cost of physical activity , .
Some studies measuring metabolic rate in CR animals
give conflicting results , and lowered metabolic rate does not
necessarily entail a prolonged life span .
However, specific metabolic rate correlates highly
with oxidative DNA damage. This is consistent with the theory that free
radical induced DNA damage may play a central role in the aging process
Body temperature, one of the biomarkers of longevity,
is linked to metabolic rate; a lowered BMR would be associated with a
slightly lowered core body temperature.
It seems logical to expect that because yoga asana is
an energy expenditure activity, it would increase the resting metabolic
rate. However, two different studies using healthy volunteers found that
the BMRs of yoga groups practicing asana, pranayama and meditation were
significantly lower than the BMRs of control groups  . Asanas when
practiced along with pranayama and meditation over a period of time
actually significantly reduce the metabolic rate  .
The metabolic rate is an indicator of autonomic
activity. The lower metabolic rates in the yoga subjects may have been
due to decreased sympathetic nervous system activity and probably, a
stable autonomic nervous system response achieved due to training in
yoga  .
A study on alternate nostril breathing found that
breathing selectively through either nostril could have a marked
activating effect or a relaxing effect on the sympathetic nervous
system; it is possible to alter metabolism by changing the breathing
Hypometabolic states have been reported in yogic
studies, and meditation has been described as a wakeful hypometabolic
state of parasympathetic dominance , . Reports exist of yogis
being buried underground in pits for many hours, and emerging unscathed.
This may be achieved by consciously and voluntarily entering a
hypometabolic state , .
This suggests not just a general lowering of BMR as a
result of practice, but in advanced practitioners, eventually a learned
ability to control normally involuntary bodily processes .
Krishnamacharya was apparently able to stop his own heartbeat and breath
for several minutes with no ill effects - he demonstrated this before a
panel of doctors at the age of 76 .
Higher levels of DHEA are associated with greater
feelings of wellbeing, higher muscle to fat ratios, and enhanced immune
DHEA also seems to increase sensitivity to insulin.
Low DHEA levels correlate with lower bone mineral density and higher
risk of osteoporosis, and also increased risk of heart disease . A
significant deficiency in DHEA in patients with several major diseases
including cancer, inflammatory diseases, type 2 diabetes,
atherosclerosis, Alzheimer's disease and cardiovascular disorders has
been described .
Levels of DHEA that occur naturally in the body
decline with age.
Calorie restriction has also been shown to increase
DHEA levels in animals. DHEA was found to be a very good marker to
measure the rates of aging in control versus calorie restricted monkeys
Most forms of exercise will raise DHEA levels ,
so practicing yoga asana would play a role in maintaining DHEA levels.
Studies have shown that meditation is associated with
increased levels of DHEA, as well as melatonin and GABA (gamma
aminobutyric acid, which reduces anxiety) , .
Older individuals practicing meditation had higher
levels of DHEA than an age-matched control group of non-meditators.