Calcium
Calcium is the most abundant mineral in the human body, with 99% stored in bones and teeth to provide skeletal strength [40]. The remaining 1% is critical for vital physiological processes including muscle function and nerve signaling [40].
The primary purpose of calcium supplementation is to prevent or correct a deficiency when dietary intake is insufficient [31]. While often used to support bone health and prevent osteoporosis, the broader benefits of supplementation are nuanced, and the decision to supplement requires careful consideration of potential risks and individual health needs [26].
Calcium's role in the body is extensive and well-understood. Beyond providing the mineral content for bone mineralization, it acts as a critical signaling molecule [6]. In the nervous system, an electrical signal triggers an influx of calcium ions that facilitates the release of neurotransmitters, enabling communication between nerve cells [50][3]. Low calcium levels can impair this process [50]. At a cellular level, calcium functions as a ubiquitous second messenger; a temporary increase in intracellular calcium can activate a host of enzymes and proteins, influencing responses like gene transcription, cell growth, and programmed cell death [45].
The most validated outcome of calcium supplementation is its effect on bone health.
- Bone Mineral Density (BMD): Studies show that increasing calcium intake through supplements can produce small, non-progressive increases in BMD of about 0.6-1.8% at sites like the hip and spine, with most of the benefit occurring in the first year [20][43]. This effect is particularly noted in postmenopausal women, where it can help reduce the rate of bone loss, and in prepubescent children, where it can increase the rate of bone mineral accrual [47][32].
- Fracture Prevention: The impact on fracture risk is less clear. Some meta-analyses report that combined calcium and vitamin D supplementation can reduce the risk of total fractures by 15% and hip fractures by 30%, an effect most pronounced in older, institutionalized individuals [25][36][16]. However, other large-scale studies found that for community-dwelling adults, supplements do not significantly reduce fracture risk [5][20].
For all these processes, vitamin D is essential, as it is required for the absorption of calcium in the gut [6][51].
A typical protocol for an individual who requires calcium supplementation, as determined by a healthcare provider, involves bridging the gap between their dietary intake and the recommended daily amount of 1,000-1,200 mg [41].
- Dosage: To optimize absorption, total supplemental calcium should be taken in divided doses of 500 mg or less at a time [6][41]. For example, if 1,000 mg is needed, one would take 500 mg in the morning and 500 mg in the evening.
- Formulation: The two most common forms are calcium carbonate and calcium citrate.
- Calcium Carbonate is inexpensive and contains 40% elemental calcium, but it requires stomach acid for absorption and should be taken with food [1][48].
- Calcium Citrate contains 21% elemental calcium and is more easily absorbed, making it a better choice for older adults or those with low stomach acid; it can be taken with or without food [1][18].
- Co-factors: Supplementation is often paired with 800-1,000 IU of vitamin D daily to ensure proper calcium absorption and maximize benefits for bone health [29][16].
A common pitfall is taking a large, single dose of calcium, which reduces absorption efficiency [6]. Another is failing to account for potential interactions with medications like thyroid hormones (levothyroxine) or certain antibiotics, which may require spacing doses several hours apart [8].
Pros
Cons
Cardiovascular Controversy: The most significant concern is a potential link to cardiovascular risk. Some meta-analyses suggest calcium supplements are associated with an approximate 15% increased risk of cardiovascular disease in healthy postmenopausal women [19][27]. The proposed mechanism is that rapid spikes in blood calcium from supplements may promote vascular calcification [22][39]. However, other major reviews have found no significant association, making the evidence conflicting [24][10][44].
Do calcium supplements cause kidney stones?
This is a common misconception. A diet low in calcium can actually increase the risk of developing the most common type of kidney stones (calcium-oxalate) [42][28]. Dietary calcium binds to oxalate in the intestines, preventing it from being absorbed and forming stones in the urine [15]. However, calcium supplements, especially when taken without food, can increase the amount of calcium in the urine and may raise the risk of stones in susceptible individuals [15][4]. Taking supplements with meals can help mitigate this risk [15].
Do calcium supplements increase heart disease risk?
The evidence is conflicting. Some meta-analyses have found that calcium supplements are associated with an approximate 15% increased risk of cardiovascular disease in healthy postmenopausal women [27][12]. The theory is that supplements cause a rapid spike in blood calcium that may contribute to arterial calcification [39][2]. However, other large systematic reviews have found no significant link between calcium supplements (taken within recommended limits) and risk of heart attack, stroke, or mortality [11][10]. Research agrees that calcium obtained from dietary sources is not associated with this risk and may even be protective [46][7].
Is it better to get calcium from food or supplements?
There is a broad scientific consensus that a "food-first" approach is superior [52][30]. The body absorbs calcium from food more efficiently, as it is consumed in smaller amounts throughout the day along with other nutrients that aid absorption [30][28]. Dietary calcium does not cause the sharp spikes in blood calcium levels associated with supplements and their potential risks [28]. Supplements should be used only to fill a documented dietary gap [52].
What is the best way to take calcium supplements?
To optimize absorption and minimize side effects, it is best to take no more than 500-600 mg of elemental calcium at one time [11][37]. If you need a higher daily dose, split it into two or more doses [49]. Calcium carbonate should be taken with food to enhance absorption, while calcium citrate can be taken with or without food [11][35]. Finally, ensure you have adequate vitamin D status, as it is essential for your body to absorb and use calcium [52].
Sources
