Scientists at Karolinska Institutet have now uncovered how this happens by identifying two relevant proteins, the production of which is stimulated by the intake of nitrate. The study found that mice supplied with nitrate in their drinking water developed significantly stronger muscles – and this at doses obtainable from a normal diet.
The researchers divided the mice into two groups, one which was given nitrate in their drinking water for seven days and a control. While spinach and beetroot are two of the main sources of nitrate, it also occurs naturally in many other leafy vegetables, such as lettuce and chard. The quantity of nitrate that the mice received was roughly equivalent to that which a person would obtain by eating 200 to 300 grams of fresh spinach or two to three beetroots a day.
A week into the experiment the team examined different muscles on the mice’s legs and feet. They found that the mice that had been on consistent nitrate had much stronger muscles, the greatest effect being observed in the extensor digitorum longus muscle, which extends down the tibia, and the flexor digitorum brevis muscle of the foot.
Continuing their study, the researchers then discovered that the nitrate mice had a higher concentration of two different proteins in their muscles, which is assumed to explain the greater muscle strength. These two proteins, CASQ1 and DHPR, are involved in the homeostasis of calcium, a critical determinant of muscle contraction.
The teams now want to take their discoveries further and study how they can be applied to people with muscle weakness.
“From a nutritional perspective our study is interesting because the amount of nitrate that affected muscle strength in mice was relatively low,” says Dr Andrés Hernández, researcher at the Department of Physiology and Pharmacology. “Translated to humans it means that we can obtain the equivalent volume by eating more of a vegetarian diet, as nitrate is found naturally in several leafy vegetables, especially in beetroot juice, for example. There are currently no dietary supplements containing nitrate.”
The study was financed by the Swedish Research Council, the Swedish National Centre for Research in Sports, Association française contre les myopathies, AFM (French Association against Myopathies) and the National Institute for Arthritis and Musculoskeletal and Skin Diseases (NIAMS).
Dietary nitrate increases tetanic [Ca2+]i and contractile force in mouse fast-twitch muscle
Journal of Physiology, Epub ahead of print 11 June 2012, doi:10.1113/jphysiol.2012.232777