Two new studies from the BMJ. The first is “Calcium intake and risk of fracture: systematic review“:
Objective To examine the evidence underpinning recommendations to increase calcium intake through dietary sources or calcium supplements to prevent fractures.
Design Systematic review of randomised controlled trials and observational studies of calcium intake with fracture as an endpoint. Results from trials were pooled with random effects meta-analyses.
Data sources Ovid Medline, Embase, PubMed, and references from relevant systematic reviews. Initial searches undertaken in July 2013 and updated in September 2014.
Eligibility criteria for selecting studies Randomised controlled trials or cohort studies of dietary calcium, milk or dairy intake, or calcium supplements (with or without vitamin D) with fracture as an outcome and participants aged >50.
The MIC would have you believe that drinking milk (ie increasing your dietary calcium intake) will protect your bones. This was a systematic review to look at RCTs or observational studies to see if that’s the case, with fracture as the endpoint. Participants had to be at least 50 years old.
They found only two RCTs of dietary calcium intake increases, with 262 participants total. There were, however, 44 cohort studies of calcium (37), milk (14), or dairy intake (8).
Let’s take calcium first. Most studies found no relationship between intake and fracture (17/21 for hip, 7/8 for vertebral, 5/7 for forearm, and 14/22 for total). For dairy, 11/13 found no association. For milk, 25/28 studies found no association. The milk emperor has no clothes.
Let’s try calcium supplementation, not from diet. There were 26 RCTs. Supplementation did reduce total fractures (RR 0.89) and vertebral fractures a little bit (RR 0.96). But there was no protection against hip or forearm fractures.
All studies were not of similar quality, though. When they considered the four RCTs at lowest risk of bias, no effect of fracture protection was seen at all, in any site.
Similar (disappointing) results were seen for calcium monotherapy and co-administered calcium and vitamin D.
Conclusion? Dietary calcium isn’t associated with a risk of fracture. There’s no evidence that increasing dietary calcium prevents fracture. Even the evidence that says that calcium supplementation prevents fracture is weak.
Study two is “Calcium intake and bone mineral density: systematic review and meta-analysis“:
Objective To determine whether increasing calcium intake from dietary sources affects bone mineral density (BMD) and, if so, whether the effects are similar to those of calcium supplements.
Design Random effects meta-analysis of randomised controlled trials.
Data sources Ovid Medline, Embase, Pubmed, and references from relevant systematic reviews. Initial searches were undertaken in July 2013 and updated in September 2014.
Eligibility criteria for selecting studies Randomised controlled trials of dietary sources of calcium or calcium supplements (with or without vitamin D) in participants aged over 50 with BMD at the lumbar spine, total hip, femoral neck, total body, or forearm as an outcome.
Pretty much the same study, but with bone density (not fracture) as the outcome of interest. In this case, though, they stuck to RCTs. They found 59 of them, both for dietary calcium (15) and calcium supplementation (51).
Increasing dietary calcium intake did increase bone mineral density (BMD) by 0.6-1.0% both at the hip and total body at one year. It also increased BMD there and at the lumbar spine and femoral neck by 0.7-1.8% at two years. It had no effect on the forearm.
Calcium supplementation increased BMD all over by 0.7-1.8% at one, two, and 2.5 years.
But these changes, while statistically significant, are unlikely to lead to any meaningful outcomes. They certainly don’t protect against fracture (see first study).
From the accompanying editorial, entitled “Calcium supplements do not prevent fractures”
By use of guidelines such as those by NOF and the International Osteoporosis Foundation (IOF), marketing now extends to all older people with dietary intakes below the recommended 1200 mg calcium and 800-1000 IU vitamin D daily. By this definition virtually the whole population aged over 50 is at risk. Most will not benefit from increasing their intakes and will be exposed instead to a higher risk of adverse events such as constipation, cardiovascular events, kidney stones, or admission for acute gastrointestinal symptoms. The weight of evidence against such mass medication of older people is now compelling, and it is surely time to reconsider these controversial recommendations.
Go tell the Milk Emperor.
