Background
The
intake of dairy products has been thought to be associated with an
increased risk of coronary heart diseases (CHD) and total mortality due
to its relatively high content of saturated fat. However, reports on
this association particularly among US adults are conflicting and
controversial. Therefore, we used data from the 1999-2010 National
Health and Nutrition Examination Surveys (NHANES) study to examine
whether consumption of total dairy and dairy subgroups was associated
with total and cause specific (CHD, cerebrovascular and cancer)
mortality. Further we carried out a systematic review and meta-analysis
of prospective studies to check for consistency with the NHANES
findings.
Methods
In
the NHANES cohort vital status through December 31, 2011 was
ascertained. Cox proportional hazard regression models were used to
relate baseline dairy intake with all-cause and cause-specific
mortality. For the systematic review PubMed, SCOPUS, Web of Science and
Google Scholar databases were searched (up to December 2017). The
DerSimonian-Laird method and generic inverse variance methods were used
for quantitative data synthesis.
Results
In
the NHANES data set of 24474 participants, 3520 deaths occurred during
follow-up. In multivariate adjusted Cox models, total mortality risk was
lower when comparing the top (Q4) with the lower (Q1) quartiles of
total dairy (hazard ratio [HR] 0.98, 95% confidence interval [CI]:
0.95-0.99) and cheese (HR: 0.92, 95%CI: 0.87-0.97) consumption. Using a
similar model, we have found a negative association between total dairy
and milk consumption with risk of cerebrovascular mortality (HR: 0.96,
95%CI: 0.94-0.98, HR: 0.93, 95%CI: 0.91-0.96, respectively), while milk
consumption was associated with increased CHD mortality (HR: 1.04,
95%CI: 1.02-1.06). The meta-analysis with 636,726 participants indicated
a significant inverse association between fermented dairy products and
total mortality (RR: 0.97, 95%CI: 0.96-0.99), while milk consumption was
associated with higher CHD mortality (RR: 1.04, 95%CI: 1.01-1.05).
These findings were robust in sensitivity analyses.
Conclusions
Among
American adults, higher total dairy consumption was associated with
lower total and cerebrovascular mortality, while higher milk consumption
was associated with higher risk of CHD. These findings do not support
dogmatic public health advice to reduce total dairy fat consumption,
although the association between milk consumption and CHD mortality
requires further study.
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