Is Viagra a new wonder diet pill?
'Viagra helps men fight the flab as well as boost their sex life,' reports the Daily Mail, somewhat prematurely, on a study involving mice.
The study aimed to examine the effect of a chemical signalling messenger (cGMP, cyclic guanosine-3',5'-monophosphate) on fat tissue commonly referred to as "white fat". The body uses chemical signalling messengers to transmit signals from one cell to another.
There are two types of fat tissue in all mammals: white adipose tissue and brown adipose tissue. White adipose tissue stores fats and is what we traditionally think of as "fat".
In contrast, brown adipose tissue generates heat from fat. Brown adipose tissue is present in higher levels in infants and plays an important role in keeping them warm. It is thought it is converted into other types of tissue as humans grow, although it has been found in adults.
The researchers wanted to see if sildenafil (the active component of Viagra) caused white fat tissue in mice to become more like brown fat tissue, a process called "browning".
They found that short-term treatment with sildenafil caused white adipose tissue to look more like brown adipose tissue. The researchers speculate that this "browning" could lead to increased energy expenditure and weight loss.
Although these results seem promising, all of the tests so far have been in mice. Further research is required to determine whether Viagra could achieve a similar effect in humans without causing any dangerous side effects or complications.
Despite the optimistic headline, the Daily Mail article warns that the public should not assume that popping a Viagra pill will help them shed the pounds.
Where did the story come from?
The study was carried out by researchers from the University of Bonn, the Federal Institute for Drugs and Medical Devices, Bonn, and the Max Planck Institute for Heart and Lung Research, Germany, and was funded by the Deutsche Forschungsgemeinschaft (DFG).
It was published in the peer-reviewed journal of the Federation of American Societies for Experimental Biology (FASEB).
The Daily Mail's headline is both inaccurate and sensationalist. Claims that Viagra "can melt away that 'spare tyre'" in men cannot be substantiated, as all the experiments were performed in mice.
What kind of research was this?
This was a laboratory and animal study both on mice and using mouse cells grown in the laboratory. The researchers were interested in the effect of the signalling messenger cGMP (cyclic guanosine-3',5'-monophosphate) on fat tissue. They were particularly interested in the effect of cGMP on white adipose tissue.
There are two types of fat tissue in all mammals: white adipose tissue and brown adipose tissue. White adipose tissue stores fats and is what we traditionally think of as "fat".
Brown adipose tissue generates heat from fat. It is found in high levels in infants, playing an important role in keeping them warm, but has also been found in adults.
The researchers state that other studies have found that treating mice and cells grown in the laboratory with certain chemicals, or exposing them to the cold, causes cells that look like brown fat cells to form in white fat tissue. These are called "beige" cells, and the process has been termed "browning".
One of the experiments the researchers performed used the chemical sildenafil, the active component of Viagra. Sildenafil inhibits, or blocks, a type of enzyme which breaks down cGMP, called cGMP-specific phosphodiesterase.
In theory, inhibiting this enzyme with sildenafil should increase the levels of cGMP, which in turn should reduce body weight and improve energy balance in mice fed a high-fat diet. The researchers tested this theory in their study.
Laboratory and animal research is the basis of scientific and medical research. However, as these experiments were all performed using either mouse cells or mice, it remains to be seen if the same effects are seen in human tissue or humans.
What did the research involve?
The researchers performed a number of experiments to determine the effects of cGMP on fat tissue. In the experiment using sildenafil (Viagra), mice were treated with 0.9% salt (placebo) or 12mg/kg/day sildenafil for seven days. The weight and body composition of the mice was examined at the end of the treatment period and white adipose tissue in the abdominal region was then examined.
What were the basic results?
The researchers found that short-term treatment with sildenafil (Viagra) did not change the body weight or body composition of the mice, meaning that the percentage of their weight due to fat and lean mass remained the same.
However, when white adipose tissue from the abdominal region was examined, the researchers found that it had taken on some of the features of brown adipose tissue. For example, the cells expressed the protein UCP-1, which is key for heat production.
The researchers found that the brown adipose tissue in the mice appeared to be unaffected by sildenafil.
How did the researchers interpret the results?
The researchers suggest that sildenafil, or other drugs that increase cGMP levels, could have anti-obesity uses. These drugs could work by causing the "browning" of white fat tissue.
Conclusion
This study found that short-term treatment with sildenafil caused white fat tissue to look more like brown fat tissue. This "browning" of fat could lead to increased energy expenditure and weight loss, as instead of storing fat, the fat is burnt to produce heat.
Although these results seem promising, all of the results so far have been obtained in mice. Further research is required to determine whether Viagra has any effect on fat tissue in humans, or if it could actually lead to weight loss.
Importantly, the effective dose given to mice was higher than the dose used to treat erectile dysfunction in men. It is therefore uncertain whether using a similar dose in men (or indeed women) could lead to unpleasant – or possibly dangerous – side effects in humans.
Further animal studies are probably required before sildenafil can be tested as a potential weight loss drug in humans, in what would most likely be phase I clinical trials.
For readers looking to lose weight, we recommend the new NHS Choices Weight Loss Guide.
