钙

钙是所有生物都需要的一种矿物质，人类也不例外。人体内的钙质有99%是储存在骨骼及牙齿里，其余的1%则于血液及其他细胞组织内 ¹。体内的钙每天会从皮肤、指甲、头发、汗水和尿液中流失。当身体得不到足够的钙质来维持它的功能，它将从钙库中提取一部分的库存，即骨骼中的钙质，这会加速骨质流失，并提高骨骼疾病的风险。因此，建议从每日均衡的饮食或补充剂中摄取足够的钙，因为钙是不能由人体自身合成的 ²。高钙食品包括乳制品、深绿色蔬菜、豆制品、钙强化谷物等其他食品。

迷思与事实

人们都以为减少钙的摄取量能降低 ‘草酸钙’ 肾结石的机率。由于草酸钙型肾结石中包含钙，多数人便认定钙是造成肾结石的罪魁祸首，但事实并非如此。钙摄取量低于推荐值不但不利于骨骼健康，还可能提高肾结石的风险 ³。

健康益处

1. 骨骼健康

• 钙对骨代谢及维持骨密度起着至关重要的作用 ⁴。临床试验显示，补充钙可以降低老年人骨折的风险 ⁵。
• 更年期妇女雌激素水平下降会导致骨质迅速流逝 ⁶。这也是为什么经历更年期的女性比男性更容易患上骨质疏松症的原因。因此，专业人士建议服用钙补充剂以降低骨质疏松症的风险 ²。

2. 牙齿健康

• 想要强壮的牙齿也需要依赖足够的钙质。不足的钙会导致整个身体的骨骼（包括牙齿）密度降低，更加脆弱，这可能导致牙齿掉落。补充钙和维生素D对保持牙齿的健康有极大的好处 ¹²。

3. 神经和肌肉功能

• 钙离子是机体各项生理活动不可缺少的离子，它负责维持正常的神经传导功能 ⁷。此外，它还负责维持正常的肌肉伸缩与舒张功能。当钙在体内中的平衡状态遭到破坏，这会干扰正常的肌肉功能和神经信号。

4. 先兆子痫

• 专家门建议摄取 1500-2000 毫克的钙，以减轻因缺钙而引起的孕妇先兆子痫的严重程度 ^9,10。

建议每日剂量

健康成年人每天需要大约 800 毫克的钙。不用乳制品，通过每日均衡饮食中可获取至少 300 毫克的钙，再加上补充剂 500 毫克的钙便有助于达到每日的钙需求量。与维生素 D 和 K2 一起服用更能促进钙的吸收 ¹¹。

参考

1. Office of Dietary Supplements – Calcium. (2021). Retrieved 1 October 2021, from https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/#en1

2. Calcium/Vitamin D Requirements, Recommended Foods & Supplements. (2021). Retrieved 1 October 2021, from https://www.nof.org/patients/treatment/calciumvitamin-d/

3. 6 Easy Ways to Prevent Kidney Stones. (2020). Retrieved 20 October 2021, from https://www.kidney.org/atoz/content/kidneystones_prevent

4. Newman, T. (2020). Calcium: Health benefits, foods, and deficiency. Retrieved 1 October 2021, from https://www.medicalnewstoday.com/articles/248958#_noHeaderPrefixedConten

5. Weaver, C. M., Alexander, D. D., Boushey, C. J., Dawson-Hughes, B., Lappe, J. M., LeBoff, M. S., Liu, S., Looker, A. C., Wallace, T. C., & Wang, D. D. (2016). Calcium plus vitamin D supplementation and risk of fractures: an updated meta-analysis from the National Osteoporosis Foundation. Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA, 27(1), 367–376. doi: 10.1007/s00198-015-3386-5

6. Song L. (2017). Calcium and Bone Metabolism Indices. Advances in clinical chemistry, 82, 1–46. doi: 10.1016/bs.acc.2017.06.005

7. Insel, P., Ross, D., Bernstein, M., & Mcmahon, K. (2011). Nutrition (4th ed.). Sudbury, Mass.: Jones and Bartlett Publishers.

8. Powers, S., & Howley, E. (2012). Exercise physiology (8th ed.). New York: McGraw-Hill Higher Education.

9. Hypertension in pregnancy. Report of the American College of Obstetricians and Gynecologists’ Task Force on Hypertension in Pregnancy. (2013). Obstetrics and gynecology, 122(5), 1122–1131. doi: 10.1097/01.AOG.0000437382.03963.88

10. WHO recommendation: Calcium supplementation during pregnancy for the prevention of pre-eclampsia and its complications. (2018). World Health Organization.

11. How much calcium do you really need? – Harvard Health. (2019). Retrieved 20 October 2021, from https://www.health.harvard.edu/staying-healthy/how-much-calcium-do-you-really-need

12. Krall, E. A., Wehler, C., Garcia, R. I., Harris, S. S., & Dawson-Hughes, B. (2001). Calcium and vitamin D supplements reduce tooth loss in the elderly. The American journal of medicine, 111(6), 452–456. https://doi.org/10.1016/s0002-9343(01)00899-3