Women’s risk for CV events decreased with higher dietary calcium intake, although there was no association between calcium intake and stroke or bone fracture, reported the research team led by the Seoul National University College of Medicine.
In men, there was no significant association between dietary calcium intake and risk of CV event, stroke, fracture or all-cause mortality, although CV event risk did show a weak increasing trend with higher intake.
“High daily dietary calcium intake was associated with a decreased risk of CVD event, but not stroke or fracture, in Korean women. In men, dietary calcium intake was not associated with CVD [event], stroke, or fracture risks,” wrote first author Sung Hye Kong.
The effect of calcium intake on CV events, particularly supplementary intake, is currently the subject of much controversy. Most previous studies have typically involved Western populations with relatively high dietary intakes; - including two large observational cohorts reporting mean intakes of around 840 milligrams per day (mg/d). By contrast, previous research suggests an average Korean intake of around 490 mg/d.
This study, involving a population with a relatively low dietary intake, may therefore add a new perspective to existing research.
“To our knowledge, only a few studies regarding the association between dietary calcium intake and CVD event, stroke, and fractures have been conducted to date using a population with low calcium intake,” explained the researchers.
The prospective study used data from the Korean Genome Epidemiology Study and analysed 2158 men and 2153 women aged between 40 and 69. Patients completed a dietary questionnaire, which was used to calculate calcium intake at baseline. Incidence of CV events, strokes and bone fractures were measured during the nine-year follow-up period.
The researchers adjusted results for covariates including age, body mass index, protein and sodium intake, fruit and vegetable intake, diabetes, hypertension and smoking status.
Prior to adjustment for covariates, the relationship between calcium intake in women and CV event risk was found to be U-shaped. Only after adjustment, did they find a decrease throughout all quartiles of intake.
The researchers also performed additional analysis examining the effect of each incremental milligram of calcium intake on CV event risk in women. Again a U-shaped relationship was found, with the graph indicating an optimum dietary intake for women of around 600mg/ day to minimise CV event risk. No corresponding figure could be for men because of the lack of association between calcium intake and CV event risk in males. A previous meta-analysis also suggested a U-shaped relationship, with CV mortality risk minimised at around 800 mg/d.
Most previous studies, but not all, involving dietary calcium have shown a protective effect of higher intakes, against CVD risk and all-cause mortality. Calcium supplementation studies have shown very mixed results.
The findings led the researchers to hypothesise that consumption of 500-1000 mg/d calcium supplements in addition to dietary sources may result in a total intake associated with a higher CV event risk. This might explain some of the adverse effects observed in supplementation trials, they argued.
The researchers highlighted that dietary calcium intake was only measured at baseline and therefore could have changed during the relatively long follow-up period. Secondly, CV events were self-reported, possibly reducing data accuracy. Thirdly, the scientists did not measure either vitamin D status or parathyroid hormone level, which are recognised to be closely linked with calcium metabolism. Vitamin K2 status was also not analysed.
“The association between high calcium intake and CVD [event] risk needs to be assessed further in additional prospective studies,” proposed the researchers.
Source: American Journal of Clinical Nutrition
Volume 106, issue 3, pp 27-34 DOI: 10.3945/ajcn.116.148171
“Dietary calcium intake and risk of cardiovascular disease, stroke, and fracture in a population with low calcium intake”
Authors: Sung Hye Kong, Jung Hee Kim, A Ram Hong, Nam H Cho, and Chan Soo Shin