For Tea drinkers, they have more or less heard the claim that “Drinking Tea causes calcium loss.”

Is this rumor true or false?

Let's delve into the facts!

1

Calcium Metabolism in the Human Body

Calcium is one of the essential elements in the human body, accounting for approximately 2% of body weight, with most of it stored in bones.

The absorption of calcium occurs throughout the gastrointestinal tract, primarily in the intestines.

(1) Effects of Calcium Deficiency on the Body

Bones are the basic framework of vertebrates and are the primary organs involved in calcium metabolism, working together with the kidneys and intestines to control the balance of calcium in the internal environment. When the body's intake of calcium is insufficient, calcium is released from the bones, increasing the risk of diseases such as osteoporosis.

(2) Factors Leading to Calcium Loss

The body's calcium mainly comes from food, and its bioavailability can be influenced by many endogenous factors such as age, disease, hormones, physiological conditions (pregnancy, breastfeeding, menopause, etc.), and gut microbiota, as well as exogenous factors like other nutrients in the diet.

Age factor: From birth to old age, there is a significant change in calcium metabolism in the human body. During growth periods, bones gradually mature, and the amount of bone calcium increases. Generally, after the age of 20, bone metabolism is in dynamic equilibrium, and after the age of 40, bone metabolism becomes negative, leading to a decrease in bone calcium.

Hormonal factor: The main hormones regulating blood calcium levels to maintain calcium homeostasis in the body are parathyroid hormone (PTH), calcitonin (CT), and vitamin D.

Disease factor: Calcium in the blood is inevitably filtered out when circulating through the kidneys, and then, under the influence of hormones related to calcium metabolism, most of it is reabsorbed by the renal tubules and returns to the bloodstream according to the body's needs. Therefore, the amount of calcium excreted in urine is closely related to the filtration by the glomerulus and the reabsorption by the renal tubules. When suffering from kidney diseases, electrolyte imbalances can occur, leading to the loss of calcium and phosphorus.

2

Rumors vs. Reality

Rumor 1:

The oxalic acid in tea forms precipitates with calcium ions in the intestine, thereby inhibiting calcium absorption.

Reality:

The oxalic acid content in each gram of tea is between 1.6-6.8 mg, and the human body's absorption rate of oxalic acid from tea is very low, at only 2.4%. However, tea also contains calcium, with each gram containing 3.1-8.0 mg of calcium. Even if oxalic acid can form precipitates with calcium, there is enough calcium in the tea itself to react with the oxalic acid, so drinking tea does not interfere with the absorption of calcium from other sources.

The Swiss physician Paracelsus once stated: “All things are poisons, for there is nothing without poisonous properties. The dose alone makes something a poison.” Compared to foods rich in oxalic acid, such as spinach, amaranth, strawberries, etc., the oxalic acid content in tea is relatively low.

Rumor 2:

Caffeine in tea increases urinary calcium excretion and may reduce bone density.

Reality:

The amount of urinary calcium excretion is primarily related to the filtration by the glomerulus and reabsorption by the renal tubules.

Early studies linking high caffeine intake to the risk of calcium loss were based on Coffee as the main source of caffeine. Caffeine accounts for approximately 3% of the composition of tea, but tea also contains higher amounts of tea polyphenols, tea polysaccharides, theanine, pigments, minerals, vitamins, etc., and their mechanisms of action on bone health are not entirely the same.

Most studies indicate that as long as the daily intake of calcium is normal, drinking tea or coffee is not associated with calcium loss.

3

Scientific Evidence

Scientific research shows that drinking tea can positively regulate blood calcium levels, improve bone density, and prevent osteoporosis.

(1) Drinking Tea Improves Bone Density

In 2025, Professor Sheng Jun's team from Yunnan Agricultural University published “Pu-erh tea Extract Ameliorates Ovariectomy-Induced Osteoporosis in Rats and Suppresses Osteoclastogenesis In Vitro” in a journal. This study used ovariectomized (OVX) rats, the best animal model for studying postmenopausal osteoporosis in women, to investigate the effects of Pu-erh tea extract (PTE) on osteoporosis induced by ovariectomy and osteoclastogenesis in vitro. The results showed: ① Pu-erh tea extract maintained the homeostasis of calcium and phosphorus and improved other biochemical parameters in the blood to varying degrees; ② significantly inhibited osteoclast differentiation without cytotoxicity; ③ suppressed the expression of key osteoclast-specific genes and proteins. Therefore, drinking tea has a positive impact on bone health and can prevent osteoporosis.

In a 2024 publication titled “Tea Consumption and Risk of Bone Health: An Updated Systematic Review and Meta-Analysis,” it was shown that individuals who drink 2-3 cups of tea per day experience faster growth rates in lumbar spine bone density compared to those who do not drink tea. Drinking tea may have protective effects on fractures, osteoporosis, hips, femurs, lumbar spines, and increased bone density.

(2) Drinking Tea Regulates Blood Calcium Levels

In the study “Observation of the Effect of Pu-erh Tea Powder on Lipids and Blood Calcium in Diabetic Patients,” 65 patients were recruited, including 36 males aged 55.5 ± 10.3 years and 29 females aged 56.9 ± 7.4 years, with a disease course ranging from 1 to 15 years. At the time of enrollment, all patients had varying degrees of lipid abnormalities, but their blood calcium levels were normal. They consumed 3-10 grams of Pu-erh tea powder daily while maintaining a reasonable diet and appropriate exercise, continuing their original medication without changes. After three months, blood samples were taken again to measure lipid and blood calcium concentrations. The results showed a significant decrease in lipids and a noticeable increase in blood calcium levels, with statistically significant differences.

(3) Functional Components in Tea that Regulate Calcium and Phosphorus Metabolism and Promote Bone Health

Flavonoids: They protect bone health through five possible mechanisms: i) reducing bone loss through antioxidant actions, ii) alleviating bone loss through anti-inflammatory effects, iii) enhancing osteoblastogenesis, iv) inhibiting osteoclastogenesis, v) modulating bone immunity.

Tea Polyphenols: They can inhibit the differentiation and generation of osteoclasts. For example, epigallocatechin gallate (EGCG), one type of tea polyphenol, can regulate the metabolism of bone cells, osteoblasts, and osteoclasts and promote osteoblastic differentiation and inhibit osteoclastogenesis by modulating receptor activator of nuclear factor-b ligand (RANKL). In vitro studies have shown that EGCG can inhibit the formation of calcium oxalate crystals in the kidneys.

Minerals: Tea is rich in minerals such as calcium and phosphorus, which can regulate bone metabolism.

Vitamins: Tea also contains essential vitamins, including vitamin C and vitamin K, which have been shown to reduce the risk of fractures.