Drinking too much milk can easily lead to kidney stones? Can patients with kidney stones take calcium supplements?

In life, we often hear that "drinking too much milk can easily cause kidney stones". So are normal people prone to kidney stones if they drink too much? Can patients with kidney stones take calcium supplements?

01

Is drinking too much milk likely to cause kidney stones?

Milk is rich in protein, fat, lactose, minerals, vitamins and various bioactive ingredients. It has high nutritional value and is known as "white blood". The mineral content is 0.7%-0.75%. 100 ml of milk contains 110 mg of calcium, which is three times the calcium content of human milk. It has a high absorption rate and is a good source of calcium in daily life. According to the "Dietary Nutrient Reference Intake for Chinese Residents", the recommended daily intake (RNI) of calcium for adults is 800 mg/day. Children and adolescents are in the vigorous growth and development period, and the recommended daily intake of calcium is 1000-1200 mg/day. A box of 250 ml of pure milk on the market normally contains about 260 mg of calcium, so a pack of milk a day will not lead to excessive calcium intake. Therefore, as long as normal people do not drink more than 800-1000 ml of milk a day, it is generally not easy to suffer from kidney stones due to excessive calcium intake.

02

What are the dietary considerations for patients with kidney stones?

First, drink plenty of water to fully dilute urine to prevent urine concentration from causing calcium salt deposition and forming stones. Second, calcium supplementation through food is the first choice, such as dairy products, tofu, soy milk, soybeans, oysters, walnuts, almonds, dried shrimps, etc. Third, patients with kidney stones should try to eat less foods containing a lot of oxalic acid, such as spinach, potatoes, wild rice stems and other vegetables. Blanching them in boiling water before eating can reduce the oxalic acid content. Fourth, you can increase the intake of foods rich in trace elements such as potassium and magnesium, such as watermelon, cantaloupe, oranges, peaches, grapes, bananas, green leafy vegetables, seeds, nuts, etc. Studies have shown that insufficient magnesium and potassium in the body may be a factor that increases the risk of kidney stones.

03

Can patients with kidney stones take calcium supplements?

Foreign studies have reported that with the improvement of people's living standards and changes in dietary structure, the clinical incidence of kidney stones is about 1%-20%, which seriously affects human health. In China, the prevalence was 5.95%, 8.86% and 10.63% from 1991 to 2000, 2001 to 2010 and from 2011 to August 2021, respectively, showing a gradual upward trend and shifting to young people. The causes of kidney stones are very complex, such as age, gender, race, and eating habits. Abnormal metabolism, long-term bed rest, nutritional deficiencies, urinary tract obstruction, and urinary tract infection are common causes of stone formation. Studies have shown that kidney stones are mainly divided into five categories, which are calcium oxalate stones, calcium phosphate stones, urate stones, magnesium ammonium phosphate stones, and cystine stones according to clinical incidence. Among them, calcium oxalate stones are the most common, accounting for about 70%-80% of kidney stones. Calcium salts are indeed the main component of kidney stones, so will calcium supplementation aggravate kidney stones? In fact, calcium supplementation is not the main cause of kidney stones. In fact, calcium supplementation can prevent the occurrence of stones. Domestic studies have shown that the incidence of kidney stones in areas with low calcium content in tap water is higher than that in areas with calcium content. A foreign study showed that the incidence of kidney stones in people who often drink milk, eat cheese and yogurt is 30% lower than that of normal people. A study in the United States showed that people who consume 1357 mg of calcium in their daily diet have a 27% lower risk of kidney stones than those who only consume 535 mg of calcium per day. In the human blood, the concentrations of calcium and oxalic acid are relatively low, and the two will not form precipitation. However, the kidneys have the function of reabsorption and can highly concentrate calcium and oxalic acid in the blood. Once the concentrations of calcium and oxalic acid are high to a certain level, calcium oxalate crystals will be formed and precipitated to form stones. However, drinking high-calcium diets such as milk allows part of the calcium to be absorbed from the intestines into the blood, and the rest is retained in the intestines and excreted from the body with feces. Reduce the absorption of oxalic acid, making it less likely to form calcium oxalate stones, thereby preventing the occurrence of kidney stones.

04

How should patients with kidney stones supplement calcium?

Be careful when choosing calcium supplements. Many drugs are metabolized by the liver and kidneys. The kidney function of patients with kidney stones is affected, so it is important to choose regular calcium supplements certified by national authorities. It is recommended to take dietary supplements half an hour after a meal. Because gastric acid secretion is low in the fasting state, it is not conducive to calcium dissociation, which in turn affects calcium absorption. In addition, calcium supplementation after meals can reduce the absorption of dietary oxalate, reduce the risk of kidney stone formation, and is not likely to cause gastrointestinal discomfort.

Author: Song Tianli, Health Manager, Member of Chinese Nutrition Society

Reviewer: Chen Ran, Associate Research Librarian (Science Communication) / Senior Engineer, COFCO Nutrition and Health Research Institute