「食・栄養と健康」社会連携講座

Department of
Food, Nutrition and Health
Inquiry 日本語

Report Sample: The Need to Correct Calcium Deficiency: Delivering Scientifically-Based Healthy Foods to Society

Current status of evidence and responses based on it

Summary

There is strong evidence, including in Japanese populations, that calcium intake reduces the risk of colorectal cancer and stroke. While there is insufficient evidence, including intervention studies, regarding the association with fractures and osteoporosis, given that calcium is the main component of bone, increased intake is expected to contribute to increased bone density and fracture prevention. On the other hand, excessive intake may increase the risk of prostate cancer and ischemic heart disease, but there is insufficient evidence for this in Japanese populations. Considering international evidence regarding overall mortality risk, it is suggested that up to about 800 mg per day, the more you take, the more beneficial it is to your health. Given that calcium intake in Japan is low compared to other countries, with an average adult intake of just under 500 mg, an increase in calcium intake as a population-based approach is desirable. While Japanese people obtain nearly 30% of their calcium from milk and dairy products, considering that milk consumption is only one-third of that in major Western countries and cheese consumption is only one-fifteenth, increasing milk and cheese consumption is key. However, given Japanese food culture, it seems realistic to further increase calcium intake from soybeans, vegetables, and seafood. Furthermore, evidence suggests that calcium supplementation may be worth considering if it is difficult to obtain 800 mg of calcium from food alone, either by adding it to food or supplementing it.

Calcium intake and health

Link to death

Current state of international evidence

A meta-analysis of cohort studies examining the association between dietary calcium and mortality risk showed that, for all-cause mortality risk, the risk decreased up to 900 mg, and then leveled off or slightly increased beyond that (Figure: Calcium intake and all-cause mortality risk). Although this study included a region-stratified analysis, the association with all-cause mortality was 0.85 (0.68-1.06) for the three European studies and 0.80 (0.52-1.23) for the two Asian studies, with no significant differences observed.

Figure: Calcium intake and all-cause mortality risk

Link to cancer

Current state of international evidence

The World Cancer Research Fund International (WCRFI) continuously conducts and publishes causal relationship assessments regarding the association between diet, nutrition, physical activity, and cancer (https://www.wcrf.org/research-policy/global-cancer-update-programme/). Its Third Report II evaluates dietary calcium and calcium supplements.

Regarding the association with colorectal cancer, 11 out of 13 cohort studies showed that a 200 mg increase in dietary calcium intake reduced the relative risk. A dose-response meta-analysis estimated the relative risk to be 0.94 per 200 mg (95% confidence interval: 0.93-0.96) (Figure: Calcium Intake and Colorectal Cancer). Stratified analyses by sex and colorectal cancer showed similar results (0.93-0.94 per 200 mg), although there was no statistically significant difference in the rectal cancer group (0.94, 0.86-1.02). Furthermore, a pooled analysis combining 10 cohort studies reported that the group with the highest dietary calcium intake had a 14% lower risk of colorectal cancer compared to the group with the lowest intake (0.86:0.78-0.95).

Mechanism analysis

The following are possible mechanisms by which calcium prevents fractures:

  • Maintaining bone density (role as structural material): Approximately 70% of bone is composed of minerals such as calcium (calcium phosphate, etc.). Sufficient calcium intake keeps the bones solid and ensures physical strength against external impacts.
  • Inhibiting bone resorption (controlling recycling): When blood calcium levels drop, the body attempts to replenish calcium in the blood by dissolving bone to maintain life (bone resorption). Sufficient calcium intake suppresses this reaction and prevents bones from becoming porous.
  • Improving bone quality: Calcium maintains normal bone reconstruction. Proper turnover replaces old, brittle bone with new, elastic bone, maintaining bone quality that is less prone to fractures.
  • Maintaining bone density (role as structural material): Approximately 70% of bone is composed of minerals such as calcium (calcium phosphate, etc.). Sufficient calcium intake keeps the bones solid and ensures physical strength against external impacts.
  • Inhibiting bone resorption (controlling recycling): When blood calcium levels drop, the body attempts to replenish calcium in the blood by dissolving bone to maintain life (bone resorption). Sufficient calcium intake suppresses this reaction and prevents bones from becoming porous.
  • Improving bone quality: Calcium maintains normal bone reconstruction. Proper turnover replaces old, brittle bone with new, elastic bone, maintaining bone quality that is less prone to fractures.

Furthermore, in preventing fractures, vitamin D, which aids in calcium absorption and deposition in bones, and vitamin K, which is involved in the activation of osteocalcin, a protein necessary for bone deposition, are considered essential.

TEST

Calcium intake of Japanese people

Current situation and trends

According to the 2023 National Health and Nutrition Survey, the average calcium intake for Japanese people was 489 mg (499 mg for men and 480 mg for women). Broken down by age group, intake was exceptionally high at 624 mg for those aged 7-14 (the compulsory education age when school lunches are provided), then decreased after age 15, falling below an average of 500 mg, but exceeding 500 mg after age 60 (Figure: Calcium Intake of Japanese People). The recommended daily intake of calcium according to the Dietary Reference Intakes 2025 is highest for those aged 12-14 (1000 mg for men and 800 mg for women), but for adults it is 750 mg for men and 650 mg for women. However, average intake at all ages is significantly lower than the recommended amount.

According to the 2023 National Health and Nutrition Survey, the average calcium intake for adults was 482 mg. The top five contributing factors were milk (14%), fermented milk/lactic acid beverages (7.2%), tofu (5.4%), other green and yellow vegetables (4.8%), and cheese (4.6%) (Figure: Sources of Calcium Intake for Japanese People (Ages 20 and Over)). Including other dairy products (2.7%), milk and dairy products account for nearly 30% of calcium intake, making them the primary source. Calcium is also obtained from vegetables, legumes, grains, and seafood, but these accounts for relatively small proportions.

Calcium intake for Japanese people was less than 300 mg before 1950, then increased to 550 mg in the 1970s, but has since leveled off or slightly decreased (Figure: Annual Trends in Calcium Intake for Japanese People). Since the mid-1990s, calcium intake has been declining across all age groups, but calcium intake from dairy products has been increasing (Figure: Annual trends in calcium intake (mg/day) by source among Japanese people).

International positioning

In 2018, the median calcium intake in G7 countries other than Japan was 711 mg in Italy, the lowest, and 1000 mg in Germany, the highest, nearly double Japan’s 512 mg (Global Dietary Database https://www.globaldietarydatabase.org/data-download) (Figure: International Comparison of Calcium Intake (G20)). Looking at calcium intake in the G20 countries, Europe and North America have the highest intake, followed by South America and the Middle East, while Asian countries have low intakes. However, Japan’s intake is slightly higher than that of China, South Korea, and India. It is noteworthy that China, which had a remarkably low intake of 134 mg in 1990, tripled to 425 mg in 2018. The low calcium intake among Japanese people is attributed to their low consumption of milk (76g, about one-third of the median of 200g in the UK, Canada, the US, and France) and cheese (2.1g, about one-fifteenth to one-twentieth of the median of 30-40g in the UK, France, the US, and Canada), which are major sources of calcium.

Recommendations based on the current state of evidence

  • Strong evidence that the risk of stroke, which significantly impacts the shortening of healthy life expectancy in Japan, decreases as calcium intake increases within the Japanese calcium intake distribution range.
  • Evidence that the risk of colorectal cancer, the second leading cause of cancer death in Japan, may decrease (prostate cancer risk may increase).
  • Evidence that the risk of fracture, which significantly impacts the shortening of healthy life expectancy in Japan, may decrease as calcium intake increases within the Japanese calcium intake distribution range.
  • Evidence that up to approximately 900-1000 mg of calcium within the international intake range reduces overall mortality risk and cardiovascular disease risk.
  • Currently, the average calcium intake of Japanese adults is 482 mg (median: 438 mg), which is low internationally and has not shown an increasing trend over time.

Based on the current evidence,

  • As a population approach, increasing the average calcium intake of Japanese people to around 800mg would contribute to extending the healthy lifespan of the Japanese population.
  • Individually, it is advisable to avoid consuming more than 1000mg.

References

  1. Wang X, et al, Dietary calcium intake and mortality risk from cardiovascular disease and all causes: a meta-analysis of prospective cohort studies. BMC Med. 2014 Sep 25:12:158.
  2. World Cancer Research Fund/American Institute for Cancer Research. Diet, Nutrition, Physical Activity and Cancer: a Global Perspective. Continuous Update Project Expert Report 2018. Available at https://www.wcrf.org/research-policy/library/third-expert-report-complete-bundle/
  3. Cho E, et al. Dairy foods, calcium, and colorectal cancer: a pooled analysis of 10 cohort studies. J Natl Cancer Inst. 2004 Jul 7;96(13):1015-22.
  4. Aune D, et al. Dairy products, calcium, and prostate cancer risk: a systematic review and meta-analysis of cohort studies. Am J Clin Nutr. 2015 Jan;101(1):87-117.
  5. Ishihara J, et al. Dietary calcium, vitamin D, and the risk of colorectal cancer. Am J Clin Nutr. 2008 Dec;88(6):1576-83.
  6. Sawada N, et al. Dairy product, saturated fatty acid, and calcium intake and prostate cancer in a prospective cohort of Japanese men. Cancer Epidemiol Biomarkers Prev. 2008Apr;17(4):930-7.
  7. Larrson SC, et al. Dietary calcium intake and risk of stroke: a dose-response meta-analysis. Am J Clin Nutr. 2013 May;97(5):951-7.
  8. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010037.pub4/full#0
  9. Umesawa M, et al. Dietary calcium intake and risks of stroke, its subtypes, and coronary heart disease in Japanese: the JPHC Study Cohort I. Stroke. 2008 Sep;39(9):2449-56.
  10. Bolland MJ, et al. Calcium intake and risk of fracture: systematic review. BMJ. 2015;351:h4580. Published 2015 Sep 29.
  11. Nakamura K, et al. Calcium intake and the 10-year incidence of self-reported vertebral fractures in women and men: the Japan Public Health Centre-based Prospective Study. Br J Nutr. 2009;101(2):285-294.
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