Effects of yoga practice on metabolic factors associated with aging

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 [2].

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 [3], [16].

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 [9].

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 abdominal circumference.

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 [18]. It has been found that there were favourable metabolic changes in overweight and underactive subjects who practiced restorative yoga [10]. 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 [9].

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 [37].

Reviews of published studies found that yoga interventions are generally effective in reducing body weight and glucose levels [41], [20], [21]. 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 health outcomes.

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 [16].

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 [26].

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 [43].

Studies indicate that pranayama and yoga asanas can be helpful in patients with lipid metabolism disorders [26], and have a positive effect on blood lipid profile, reducing cholesterol [41], [20], [21].

Melatonin

Melatonin is produced by the pineal gland, and appears to have anti aging properties [36], likely due to its antioxidant properties. It is also a natural immune enhancer and has been shown to extend longevity in some animal studies [22]. Higher melatonin levels are also associated with an increased sense of well being.

Melatonin is released mainly at night during sleep. Moderate physical activity has been shown to increase production of melatonin [35].

Calorie restriction has been shown to prevent the usual age related decline in melatonin levels in monkeys [30].

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 [19], [40], [34].

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 score.

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 [19].

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 [40].

Longer term studies are required to ascertain whether the higher melatonin levels in yoga practitioners and meditators are sustained.

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 [27], [15].

Some studies measuring metabolic rate in CR animals give conflicting results [24], and lowered metabolic rate does not necessarily entail a prolonged life span [15].

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 [1].

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 [7] [8]. Asanas when practiced along with pranayama and meditation over a period of time actually significantly reduce the metabolic rate [7] [8].

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 [7] [8].

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 pattern [39].

Hypometabolic states have been reported in yogic studies, and meditation has been described as a wakeful hypometabolic state of parasympathetic dominance [44], [8]. 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 [6], [44].

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 [44]. 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 [13].

Dehydroepiandrosterone (DHEA)

Higher levels of DHEA are associated with greater feelings of wellbeing, higher muscle to fat ratios, and enhanced immune function.

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 [23]. 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 [32].

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 [25].

Most forms of exercise will raise DHEA levels [35], 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) [33], [17].

Older individuals practicing meditation had higher levels of DHEA than an age-matched control group of non-meditators. [33], [17]

View the original article here