Indtag af mejeriprodukter og udvikling af hjerte-kar-sygdomme, type 2 diabetes og metabolisk syndrom

In Denmark, the Danish Veterinary and Food Administration (DVFA) is responsible for the official national dietary guidelines. In 2011, DVFA decided to initiate an update of The Official Dietary Guidelines 2005. The work resulted in 10 recommendations, which DVFA launched in 2013 (The Official Dietary Guidelines 2013). One of the 10 recommendations concerns the nutrient saturated fat: “Eat less saturated fat”. Another recommendation concerns intake of low-fat dairy products: “Choose low-fat dairy products”. The primary reason why DVFA recommends the population to decrease intake of saturated fat is that intake of saturated fat increases the risk of ischemic heart disease (IHD), mediated partly by the effect on low-density lipoprotein cholesterol in the blood, which is an important risk factor for development of atherosclerotic cardiovascular diseases, among these IHD. The reason why DVFA recommends the population to choose the low-fat dairy product variants of dairy products is that the low-fat variants have a lower content of saturated fat compared with the high-fat variants.

During the last years, however, nutritional research has focused on the effect of intake of whole foods and dietary patterns on health as nutrients, other biologically active components, their mutually interplay as well as the physical structure of the food (for example solid versus liquid) probably all are of importance.

The aim of the current project is therefore to review the scientific literature on intake of dairy products and development of cardiovascular diseases, type 2 diabetes (T2D) and metabolic syndrome (MetS), as such a review of the scientific literature could contribute to update the scientific evidence of DVFA’s recommendation of intake of dairy products.

We used similar methods to identify, select and review literature as used when updating The Official Dietary Guidelines 2005. Most emphasis was put on conclusions in systematic expert reports, where independent organizations and health authorities systematically have collected, analysed and evaluated existing knowledge in the area of diet and development of lifestyle-related diseases, and used methods for evaluation of causality as described by World Cancer Research Fund/American Institute for Cancer Research. Other literature was used to ensure quality such as consensus reports and reviews.

MEDLINE (via PubMed) and EMBASE were searched to identify systematic expert reports, consensus reports and systematic reviews in the areas of diet and development of cardiovascular diseases, T2D and MetS published in the period after the scientific evidence of the 2013 guidelines. Furthermore, we conducted a systematic review of cohort studies on the associations between total intake of dairy products and intake of dairy product subgroups and development of atherosclerotic cardiovascular diseases (IHD, ischemic stroke and peripheral artery disease) and hemorrhagic stroke. The cohort studies were systematically identified, analysed and evaluated as described in Preferred Reporting Items for Systematic Reviews and Meta-Analyses: the PRISMA Statement. Associations between the exposures:

- milk
- low-fat milk
- high-fat milk
- yoghurt/other soured milk products
- low-fat yoghurt/other soured milk products
- high-fat yoghurt/other soured milk products
- cheese
- low-fat cheese
- high-fat cheese
- butter

and the outcomes

- IHD
- peripheral artery disease
- ischemic stroke
- hemorrhagic stroke

were investigated using meta-analysis to combine the results from the cohort studies.

Overall, the literature on intake of dairy products and development of cardiovascular diseases, T2D and MetS suggests that intake of milk, yoghurt/other soured milk products, cheese and butter is associated with lower risk, or that there is no association. In our systematic review, however, we found that higher intake of high-fat milk is associated with a higher risk of IHD.

In our systematic review, we reviewed cohort studies on intake of dairy products and risk of atherosclerotic cardiovascular diseases and hemorrhagic stroke. Associations between intake of low-fat or high-fat milk and intake of low-fat or high-fat yoghurt/other soured milk products have not been investigated in previous systematic reviews. Future cohort studies, especially studies of substitutions between dairy product subgroups, are warranted as the effect of a given dairy product depends on the replacement food or mix of other foods. Findings from studies on substitutions between dairy product subgroups can be used directly in food-based dietary guidelines for the population (for example the effect of substitution of high-fat milk with low-fat milk). Only few studies have specified substitutions. This means that a given dairy product was compared with a mix of other foods in most of the included cohort studies. Furthermore, studies which investigate sex-specific differences are especially warranted. In high-low meta-analysis, we found that a higher intake of cheese is associated with lower risk of IHD among women, but not among men. In linear dosis-response meta-analysis, higher intake of cheese was associated with lower risk of IHD and there were no indication of sex-specific differences. Finally, only few cohort studies on intake of dairy product subgroups and development of the subtypes of stroke (ischemic and hemorrhagic) have been conducted, and no studies on peripheral artery disease were identified. More studies are warranted.

We did not identify any systematic reviews which have reviewed the literature on:

- intake of low-fat or high-fat milk and risk of MetS
- intake of low-fat or high-fat yoghurt/other soured milk products and risk of T2D
- intake of low-fat or high-fat cheese and risk of T2D or MetS
- intake of butter and risk of MetS

Furthermore, we did not identify any systematic expert reports on cardiovascular diseases, T2D or MetS.