Health news - Weight gain linked to kidney stones
02 February 2005 - written by Bupa's Health information team
People who gain a lot of weight during adulthood may have a greater risk of developing kidney stones, according to a new study published in the 26 January 2005 edition of the Journal of the American Medical Association (JAMA).1
What did the study show?
The study showed that men who had gained weight since the age of 21 were 39 percent more likely to develop kidney stones than men whose weight had not changed during adulthood.
Similarly, women who had put on weight since the age of 18 were 70 to 82 percent more likely to develop kidney stones than women who had stayed about the same weight.1
What are kidney stones?
Kidney stones are hard stone-like formations that can develop in the kidneys, the bladder or the ureters (the tubes that carry urine from the kidneys to the bladder). They are formed out of calcium crystals found in the urine. In most cases, the crystals are tiny, harmless and pass out of the body unnoticed. But sometimes the crystals build up and form stones that can reach the size of potatoes.2,3
What causes kidney stones?
Kidney stones often develop for no reason. Stones are more likely to develop when the salts and minerals that are normally found in the urine become out of balance, making the urine more concentrated. This could be caused by:
- living in a hot climate or working in a hot environment, where you lose more fluid as sweat and less as urine
- not drinking enough fluid
- having a very high salt intake
Urine and kidney infections can also cause stones to develop.2,3
How common are kidney stones?
Men are three times more likely to get a kidney stone than women. It is thought that around three in 20 men and one in 20 women in the UK develop a stone at some time in their life. Stones can occur at any age but are more common in middle age.2,3
How was the study carried out?
The study recorded the number of kidney stones that developed in 45,988 men and 195,635 women over 46 years. When the study began, men were aged between 40 and 75 years old. Women were aged between 27 and 59 years old.1
How did weight gain affect the formation of kidney stones?
Men who had gained more than 15.9kg (two and a half stone) since the age of 21 were 39 percent more likely to develop kidney stones than men whose weight had not changed over the same period of time.1
Similarly, women who had put on more than 15.9kg (two and a half stone) since the age of 18 were 70 to 82 percent more likely to develop kidney stones than women who had stayed about the same weight.1
Why might weight gain be linked to kidney stone formation?
It is not certain why there may be a link between weight gain and the likelihood of developing kidney stones.
People who gain weight during adulthood tend to gain fat rather than muscle. People who carry a lot of body fat and have an increased body weight are described as obese.
Obese people are often insulin resistant. This means that their bodies are not producing enough insulin or the insulin isn't working properly.
Insulin is a hormone that controls the level of glucose (sugar) in your blood and it is important that it works properly. When it doesn't, the body passes the extra sugar out in the urine.4,5 The extra sugar may affect the balance of salts and minerals in the urine, making kidney stones more likely to develop.1
If I lose weight will I lower my risk of developing kidney stones?
According to this study, losing weight during adulthood was not associated with a reduced risk of developing kidney stones. However, very few people who took part in this study lost weight during adulthood. More research is needed.
How do I know if I've got kidney stones?
A kidney stone may cause no symptoms and no problems so you won't even know it's there.
If a stone gets stuck in a kidney or one of the ureters it may cause pain in the side of the stomach or the back.
Other symptoms include:
- severe pain spreading from the stomach down into the groin (as the stone is squeezed towards the bladder) - known as renal colic
- nausea or vomiting as a result of the pain in your stomach or groin
- blood in your urine2
How are kidney stones treated?
No treatment may be needed for stones that sit in the kidney without causing any harm. Stones that cause renal colic are usually small and pass out in the urine in a day or two, though your doctor may prescribe strong painkillers to ease the pain.
A larger stone may become stuck in the kidney or ureters. An operation may be needed to remove it to stop it causing problems.
In some cases, shock wave treatment may be used. This uses ultrasound waves to break up a large stone, so that the smaller broken fragments will then pass out with urine.2
What can I do to prevent kidney stones?
Half of people who get a kidney stone will get another one within 10 years.2 There are some things you can do that may prevent you from getting another one:
- drink lots of fluid, mainly water, to keep your urine diluted
- eat a healthy balanced diet with calcium but avoid calcium supplements
- don't eat too much salt - less than 6g (about a teaspoon) a day2,3
This study also suggests that you should:
- avoid weight gain of more than two and a half stone at any stage during adulthood (except during pregnancy)
- avoid being obese
Further information
Bupa resources:
External resources:
- The National Kidney Research Fund
www.nkrf.org.uk - UK National Kidney Federation
www.kidney.org.uk
References
- Taylor EN, Stampfer MJ, Curhan GC et al. Obesity, weight gain, and the risk of kidney stones. JAMA 2005;293:455-462.
- Patient UK. Kidney stones.
http://www.patient.co.uk - Royal Infirmary of Edinburgh Renal Unit. Kidney stones.
http://renux.dmed.ed.ac.uk/EdREN/index.html - British Nutrition Foundation. Diabetes.
http://www.nutrition.org.uk - Diabetes UK. What is diabetes?
http://www.diabetes.org.uk
All websites accessed on 27 January 2005
