Calcium Supplements
Side Effects —
What the BMJ
Study Found
A 30% increased heart attack risk in 12,000 patients — what the research shows and how to supplement calcium safely
Calcium supplements are taken by millions of people as a routine health precaution — particularly by older adults managing bone density and osteoporosis risk. The assumption is straightforward: calcium is good for bones, so a calcium supplement must be beneficial. For most people, that assumption has never been examined carefully.
Research published in the British Medical Journal suggests it deserves to be. A study examining 15 separate trials and more than 12,000 patients found a significant association between regular calcium supplementation and increased heart attack risk — a finding significant enough that the researchers called for a reassessment of the widespread use of calcium supplements in osteoporosis prevention.
What the Auckland and Aberdeen
research teams found.
The study was conducted by research teams from the Universities of Auckland and Aberdeen. Rather than running a single new trial, the researchers analysed fifteen existing studies that had examined rates of heart attacks, strokes, and deaths in people taking calcium supplements — a methodology known as a meta-analysis, which pools data across multiple studies to identify patterns that individual trials may not be large enough to detect reliably.
Fifteen studies. 12,000 patients. A 30% increased heart attack risk in regular calcium supplement users.
Patients taking 500mg or more of calcium daily were found to be approximately 30% more likely to experience a heart attack than non-supplement users.
166 patients on calcium supplements had a heart attack per comparable group, versus 130 who were not supplementing — a meaningful difference across a large patient population.
The researchers concluded: "A reassessment of the role of calcium supplements in the prevention and treatment of osteoporosis is warranted" and noted that "calcium levels have been positively associated with an increased incidence of heart attack." The study specifically excluded patients who were also taking vitamin D — a detail with significant practical implications covered in the three-step guide below.
Previous studies had produced conflicting results on whether calcium supplements protect against or worsen cardiovascular risk. The Auckland and Aberdeen meta-analysis was designed specifically to resolve this conflict — and its findings, while not definitive, are significant enough to warrant careful consideration from anyone taking calcium supplements regularly, particularly older adults already managing cardiovascular risk factors.
Cardiovascular health is directly relevant to the long-term training life this site is built around. For the complete picture on heart attack risk factors and how to manage them alongside a training programme, see the heart attack risk factors page.
The calcium supplement side effects
can be managed — here is how.
The research does not suggest that calcium is harmful or that supplementation should be abandoned entirely. It suggests that the way calcium is supplemented matters — and that combining calcium with vitamin D, managing daily intake sensibly, and prioritising food sources over pills reduces the cardiovascular risk the research identified.
-
Combine calcium with vitamin D
Vitamin D is required for the effective absorption of calcium from the digestive tract into the bloodstream. Without sufficient vitamin D, calcium supplementation is less effective and may contribute to the elevated circulating calcium levels that the research associated with increased cardiovascular risk. Critically, the Auckland and Aberdeen study excluded patients who were also taking vitamin D — meaning the 30% increased risk figure applied specifically to people taking calcium alone.
The good news is that most people with reasonable sun exposure are producing adequate vitamin D naturally through UV action on the skin. For those who require a supplement — particularly in winter months or for people with limited sun exposure — an optimal level is approximately 25 mcg (1,000 IU) daily. Anyone considering vitamin D supplementation should discuss appropriate levels with their GP, as requirements vary significantly between individuals.
-
Understand your daily calcium target
The Food Standards Agency recommends that adults obtain 700mg of calcium per day — an amount that should ideally come from dietary sources rather than supplementation. For those specifically seeking to reduce osteoporosis risk, doctors may recommend between 800mg and 1,200mg daily, with the additional amount coming from a supplement only when dietary intake is genuinely insufficient to reach the target.
The practical implication is that calcium supplementation should not be treated as a routine addition on top of an already calcium-adequate diet. It should be used to address a specific, identified dietary shortfall — and the total daily intake including dietary calcium should be calculated before any supplementation dose is determined.
-
Prioritise calcium from food
Nutrients absorbed from whole food sources are generally better assimilated than those from isolated supplements — and calcium is no exception. Prioritising dietary calcium sources both reduces the need for supplementation and delivers calcium in a form the body handles more naturally. A calcium-rich diet also delivers the co-factors — magnesium, vitamin K2, and phosphorus — that support calcium's role in bone health and reduce the risk of calcification in soft tissue.
Excellent dietary calcium sourcesFoods that provide substantial calcium alongside broader nutritional value.
Dairy — milk, cheese, yoghurtThe most concentrated and bioavailable dietary calcium sources available. Full-fat dairy also provides vitamin K2.
Green leafy vegetablesKale, bok choy, and broccoli provide meaningful calcium alongside vitamins C and K. Spinach contains calcium but absorption is reduced by oxalates.
Oily fish with edible bonesCanned sardines and salmon with soft bones provide calcium alongside omega-3 fatty acids and vitamin D.
Tofu and fortified foodsCalcium-set tofu is an excellent source, particularly for those with dairy restrictions. Fortified plant milks and cereals also contribute meaningfully.
This page summarises published research findings for general information purposes and is not medical advice. If you are currently taking calcium supplements — particularly if you have existing cardiovascular risk factors — discuss your supplementation with your GP before making any changes. Individual calcium requirements vary significantly depending on age, dietary intake, bone density, and medical history.
Supplement intelligently. Supplement specifically. Supplement to fill genuine dietary gaps rather than as routine insurance. The same minimum effective dose principle that governs training governs supplementation — enough to address the specific deficiency, nothing beyond what that requires. For the complete supplement framework, see the best muscle building supplements page.