Diet, Blood Cholesterol, Blood Pressure and Risk of Stroke: Part II

In Part I I reviewed evidence showing that while randomized controlled trials found that lowering LDL cholesterol significantly reduces the risk of coronary heart disease, ischemic stroke and all-cause mortality, but has little appreciable effect on hemorrhagic stroke, prospective cohort studies found suggestive evidence that serum cholesterol, including LDL and possibly triglycerides and the risk of hemorrhagic stroke is modified by blood pressure. The largest meta-analysis of prospective studies found that while serum cholesterol was inversely associated with risk of hemorrhagic stroke mortality in participants with high blood pressure, in participants with near optimal or ‘physiological’ blood pressure, lower cholesterol was actually associated with a significantly reduced risk of hemorrhagic, ischemic and total stroke mortality. Furthermore another very large prospective study found suggestive evidence that the inverse association between cholesterol and risk of hemorrhagic stroke confined to participants with hypertension may not be causal but acts as a marker of binge drinking.
Taking this potential modification by blood pressure and risk of stroke into consideration, as blood pressure is universally high in developed nations among people in the age range most susceptible to stroke, this may result in biasing the results of studies towards finding a lower risk of stroke for dietary changes that raise cholesterol. Therefore this justifies considering this potential bias when evaluating the evidence regarding dietary changes and the risk of stroke.

Foods rich in fiber and flavonoids may lower blood pressure and risk of stroke*

Red Meat

Despite the possibility of the above mentioned bias, a recent meta-analysis of 6 prospective studies including >329,000 participants and >10,600 cases of stroke found that each per-day serving increase of fresh red meat and processed meat was associated with a 11% and 13% increased risk of stroke respectively, without heterogeneity among studies.1 The authors not only explained that these findings could partly be attributed to saturated fat, dietary cholesterol and sodium content in fresh red meat and processed meat, but also provided the following explanation regarding how these findings may be in part explained by intake of heme iron:
Moreover, red meat is a source of heme iron. It is well-known that iron is a redox-active metal that catalyzes the formation of hydroxyl free radicals in the Fenton reaction. High doses of iron may lead to oxidative stress, a state with increased peroxidation of lipids, protein modification, and DNA damage. If continued for a long time, oxidative stress induced by iron may lead to the development of many diseases, such as cardiovascular disease, type II diabetes, atherosclerosis, neurological disorders, and chronic inflammation.

Don Matesz previously posted aninformative reviewaddressing the evidence on the absorption animal and non-animal sources of iron and the risk of developing chronic and degenerative diseases. Similarly, Dr. Michael Greger reviewed the evidence of absorption of heme and non-heme iron and the associated risks (video below).