Vitamin C May Cause Kidney Stones, Other Problems
Vitamin C has a reputation as a healthful vitamin, associated with sunshine and oranges, but a downside may be kidney stones. It seems that too much of a good thing can turn sour, and high doses of vitamin C may not only cause kidney stones, but other problems as well.
Men have a risk of kidney stones
Before looking at the various health issues associated with high doses of vitamin C, let’s look at the new research from Karolinska Institutet in Stockholm, Sweden. The eleven-year follow-up study evaluated data from 48,850 men ages 45 to 79, and specifically the 436 who developed kidney stones.
Under the leadership of Laura D.K. Thomas, MSc, an investigative team considered data only from men who had taken vitamin C supplements and no others. For comparison, the researchers also repeated their evaluation using data from men who had taken multivitamins only.
The authors found that men who took high doses (about 1,000 milligrams [mg]) of ascorbic acid (vitamin C) daily had a significant twofold increased risk of developing the painful stones. These findings “may not be generalizable to women,” who tend to be at less risk of developing kidney stones, according to the researchers.
The authors also noted that men who used multivitamins did not show the same increased risk of kidney stones. Another important bit of information they shared is that since the risk of kidney stones associated with ascorbic acid may depend on other nutrients consumed at the same time plus the dose, their findings “should not be translated to dietary vitamin C.”
Vitamin C and risks of high intake
Vitamin C is a water soluble vitamin, which means it dissolves easily, is not stored in the body, and is quickly eliminated from the body in the urine. Thus vitamin C should be replaced regularly. The recommended daily allowance for vitamin C is at least 75 mg for women who don’t smoke and 90 mg for nonsmoking men. Both men and women should add an extra 35 mg per day if they smoke.
The tolerable upper intake level of vitamin C for adults is 2,000 mg daily, and most people don’t suffer any significant side effects if they stay below that level. However, there are risks for others.
For example, some individuals experience gas, abdominal upset, nausea, vomiting, diarrhea, and increased urination when taking 500 mg to 1,000 mg or more daily. The risks for other people can be more serious. Here are a few examples.
- Kidney problems. In addition to the increased risk of kidney stones noted in men in the above study, another caution is extended to individuals who have existing kidney problems. Use of vitamin C supplements in such persons may elevate oxalate levels in the urine and result in calcium oxalate kidney stones, the most common type of kidney stones. Oxalate is found naturally in many fruits, vegetables, nuts, and chocolate, and is produced by the liver as well.
- Allergies. Anyone who has a corn allergy should check their vitamin C supplements, as some are made from corn.
- Heart disease in women. Vitamin C supplements may be harmful for some women, especially postmenopausal women who have diabetes. A study of more than 1,900 postmenopausal women with diabetes found that those who had the highest intake of vitamin C (more than 300 mg daily) from supplements—but not food—had an increased risk of death from cardiovascular disease. This risk was not seen in nondiabetic women.
- Blood thinning effect. High doses of vitamin C can interfere with the blood thinning benefits of anticoagulants such as warfarin. Anyone who has been prescribed blood thinners should consult their healthcare provider before taking vitamin C supplements.
- Diabetes. Taking high doses of vitamin C may have an impact on blood glucose (sugar) levels in people with diabetes and thus affect their need for antidiabetes medication. If you have diabetes, you should talk to your doctor before taking vitamin C supplements.
- Other health conditions. Anyone who has a medical condition associated with acid loading, such as gout, cirrhosis, paroxysmal nocturnal hemoglobinuria, or renal tubular acidosis should not take high doses of vitamin C. Again, a medical professional should be consulted for taking vitamin C supplements.
Vitamin C is a potent antioxidant and a nutrient necessary for numerous bodily functions, including the growth and repair of body tissues, iron absorption, supporting the immune system, assisting with wound healing, and maintaining bone health, among other essential tasks. As an anti-inflammatory and antioxidant, it helps protect the body against damage from harmful molecules called free radicals and thus helps fight off disease.
Yet too much vitamin C in the form of supplements may be harmful. The most healthful way to get the vitamin C you need is through food—lots of fresh fruits and vegetables—although you should consult your healthcare provider about a vitamin C supplement if you wish to take one.
Lee D-H et al. Does supplemental vitamin C increase cardiovascular disease risk in women with diabetes? American Journal of Clinical Nutrition 2004 Nov; 80(5): 1194-1200
Thomas LDK et al. Ascorbic acid supplements and kidney stone incidence among men: a prospective study. JAMA Internal Medicine 2013; 1-2. DOI:10.1001/jamainternmed.2013.2296