Dietary guidelines recommending low-fat dairy products in stroke prevention have been called into question by the findings of this large-scale Danish study. It found that substituting whole-fat fermented milk in place of other dairy types – including low-fat milk – is associated with a reduced risk of ischaemic stroke.
Previous evidence regarding the association between dairy products and stroke has been inconclusive. Intake of low fat dairy products and of whole-fat dairy products have each been associated with reduced risk of stroke, although most studies have found no link between either type.
The authors of this study aimed to help clear up this confusion by investigating the effects on stroke rate of substituting between dairy product groups. Their study included 55,211 Danish men and women aged 50-64 years who had not previously had a stroke. The participants were asked to complete a food frequency questionnaire at the start of the study.
During a median follow up of 13.4 years, the authors identified 2272 strokes within their study cohort. Of these cases, 1870 were ischaemic strokes and 389 were haemorrhagic.
Different dairy types were associated with different rates of ischaemic stroke risk
The authors analysed the effects of substituting between dairy subtypes by comparing intakes reported by the participants in their food questionnaires. This allowed them to investigate the rate of stroke associated with 1 serving/day higher intake of a specified dairy product subgroup and a 1 serving/day lower intake of another specified dairy subgroup.
While they found no association between switching dairy products and haemorrhagic stroke, three was a very different picture for ischaemic stroke. Here, diverse types of dairy products seemed to have different associations with stroke risk.
Switching to whole-fat fermented milk was associated with lower stroke risk
Substituting whole-fat fermented milk in place of low-fat milk, whole-fat milk, or buttermilk was associated with a lower rate of ischemic stroke.
In contrast, substituting semi-skimmed fermented milk or cheese in place of whole-fat fermented milk was associated with a higher rate of ischemic stroke.
Associations with dairy products may vary according to stroke sub-types
When analysing different subgroups of ischaemic stroke, the authors found a lower rate of large artery atherosclerotic stroke when whole-fat fermented milk was substituted in place of low- or whole-fat milk or buttermilk. This suggests that whole-fat fermented milk might influence atherosclerosis, say the authors.
A similar pattern of associations was found for lacunar stroke. However, for cardioembolic stroke – for which atrial fibrillation is a risk factor – semi-skimmed fermented milk seemed to hold an advantage when substituted in place of low- or whole-fat milk or buttermilk.
Why might fermented milk be more favourable than milk?
The reasons why fermented milk products might be more favourable than milk against stroke risk may lie in the composition of dairy fat, say the authors. Dairy fat contains conjugated linoleic acid which, evidence suggests, may have several anti-atherosclerotic benefits including changes in body fat, lipid profile and blood pressure. Fermented milk products contain probiotic bacteria, which may increase the amount of conjugated linoleic acid contained in the dairy product.
Another possible explanation is in the association seen in previous research between milk intake and a biomarker of oxidative stress – whereas fermented milk intake has been negatively associated with this marker.
Further research to investigate the effects of substitutions between dairy products are needed to confirm these findings, the authors conclude.
Find out more: read the original article.
Source: Ibsen DB, Laursen ASD, Lauritzen L, et al. Substitutions of dairy product intake and risk of stroke: a Danish cohort study. Br J Nutr. 2017 Dec;118(11):989-997.