Doctors have long puzzled over the link between high-salt diets and increased incidence of problems like osteoporosis and kidney stones.
Now, Canadian researchers may have uncovered the reason.
Using animals and cells in a lab, researchers have discovered that a molecule in the body that controls the movement of sodium also appears to be responsible for the movement of calcium.
The finding is significant because it helps explain why calcium as well as sodium is flushed out of the body through urine. When sodium levels in the body are high, excess amounts are lost in urine; a proportionate amount of calcium is also excreted in urine, which the researchers now believe is because they are controlled by the same molecule.
"It's definitely a huge stepping stone and leads to an area that needs to be explored and developed and has the potential for therapies," said Todd Alexander, researcher in the University of Alberta's faculty of medicine and dentistry and lead author of the study, published in the American Journal of Physiology – Renal Physiology.
People who consume too much sodium face an increased risk of kidney stones because their urine contains too much calcium, which can lead to the formation of crystals or stones. Similarly, the loss of too much calcium through urine can also increase a person's risk of developing osteoporosis, a disease characterized by thinning, fragile bones.
In the study, researchers looked at mice and possum kidney cells. They manipulated the samples so they didn't have the sodium- and calcium-controlling molecule. They found the samples were unable to absorb or retain calcium, leading to thinning bones, which suggests the molecule plays a pivotal role in calcium regulation.
Dr. Alexander noted that while the relationship between sodium and calcium levels in the body appears to be regulated by this special molecule, work still needs to be done to further understand what that means, and how those findings might be used to develop potential treatments.
He added this work is important because of the high amount of sodium in the average person's diet.
There is growing concern among many doctors and public health professionals over how much salt Canadians eat and the damage it is doing to their health.
The average Canadian consumes 3,400 milligrams of sodium, more than double the recommended daily intake, which is 1,500 milligrams for people between ages 9 and 50. This daily average also far exceeds the upper tolerable limit of 2,300 mg, beyond which the risk of health issues, such as heart disease, kidney problems and osteoporosis, starts to increase.
Many people aren't aware they are consuming dangerously high amounts of sodium because much of it is added to food products before we buy them. Most people think of potato chips and pizza when it comes to high-sodium fare. But few realize that most grocery store staples, such as bread, dressings, soups, sauces, frozen meals and even breakfast cereal, are often very high in sodium.
The federal government assembled a working group in 2007 to address this issue. The group produced a series of recommendations, including placing maximum limits on the amount of sodium companies are allowed to add to food products. The working group even went so far as to come up with draft targets for the food industry.
But months later, Health Canada disbanded the task force and abandoned the draft targets that had been created. The department is instead proposing guidelines that would encourage food manufacturers to voluntarily decrease sodium levels, but would still allow higher levels to remain in some products.