Alzheimer's Disease and Dementia
Alzheimer's disease is the most common form of dementia in the elderly. The cause of Alzheimer's disease is still unknown and there is no cure for the disease yet despite 100 years of extensive research. The possibility that the risk for Alzheimer's disease can be reduced by diet or lifestyle is of great importance and suggests a preventative treatment in Alzheimer's disease.

Epidemiological data indicate that low intake of omega 3 fatty acids is a readily manipulated dietary risk factor for Alzheimer's disease. Animal studies have confirmed the deleterious effect of omega 3 fatty acid depletion on cognition and on dendritic scaffold proteins.

The Cardiovascular Health Cognition Study compared associations of lean fish vs fatty fish (tuna, salmon or other fish) intake with dementia, Alzheimer’s disease, and vascular dementia, and in relation to APOE epsilon4 status. Although consumption of lean fried fish had no protective effect, consumption of fatty fish more than twice per week was associated with a reduction in risk of dementia by 28% and Alzheimer’s disease by 41% for those without the APOE epsilon4 allele in comparison to those who ate fish less than once per month.

In a systematic review of the literature to establish the association between eating fish or taking long-chain omega-3 fatty acid supplements and the risk of cognitive decline or Alzheimer’s disease it was concluded that there is a role for long-chain omega-3 fatty acids in slowing cognitive decline in elderly individuals without dementia, but not for the prevention or treatment of dementia, including Alzheimer’s disease.

Researchers have found that most old people with Alzheimer's disease tend to have low levels of a protein called LR11 that prevents amyloid formation. Studies have shown that increased DHA consumption resulted in an increase of the LR11 protein. Researchers have also found that DHA also reduced levels of tau protein in an animal model. Tau is another substance that builds up in Alzheimer's disease and damages brain cells essential for learning and memory.

Cardiovascular Health
Researchers have found that a diet rich in fish oils can prevent the accumulation of fat in the aorta, the main artery leaving the heart. The researchers found that the fatty acids contained in fish oil markedly inhibit the entry LDL cholesterol into arteries and, as a result, much less LDL cholesterol collects in these vessels.

In an 8-week study of 324 young overweight individuals, it was concluded that salmon consumption three times per week can decrease diastolic blood pressure similar to fish oil supplementation and significantly more than lean fish during an energy restricted diet.

Modest consumption of fish (1-2 servings/wk), especially species such as salmon that are higher in the omega 3 fatty acids EPA and DHA, reduces risk of coronary death by 36% and total mortality by 17%.

Cancer Prevention
Data from a population-based case-control study suggest that a diet high in fish could be protective against lymphohematopoietic cancers and confirm the reduced risk among fish workers.

A study examined the association between fish omega-3 fatty acids intake and the risk of breast cancer in a case-control study of 358 women. The results suggested that high consumption of fatty fish is associated with a reduced risk for breast cancer, and that the intake of omega-3 fatty acids from fish is inversely associated with postmenopausal breast cancer risk.

The relation between frequency of consumption of fish and risk of selected neoplasms was analyzed by using data from an integrated series of case-control studies conducted in northern Italy between 1983 and 1996. There was a consistent pattern of protection against the risk of digestive tract cancers with fish consumption: oral cavity and pharynx, esophagus, stomach, colon, rectum, and pancreas. There were inverse trends in risk of larynx, endometrial and ovarian cancers and multiple myeloma.

In a 5 year prospective study of 478 040 men and women from 10 European countries who were free of cancer at enrollment it was confirm that colorectal cancer risk is inversely associated with fish intake.

Researchers assessed dietary intake of fish among 1,499 incident prostate cancer cases and 1,130 population controls in Sweden. Eating fatty fish (e.g., salmon-type fish) once or more per week, compared to never, was associated with reduced risk of prostate cancer.

In another study, researchers performed a case-control analysis of 466 men diagnosed with aggressive prostate cancer and 478 healthy men. Men with low long chain omega-3 fatty acid intake and the variant rs4647310 in COX-2, a known inflammatory gene, had a more than five-fold increased risk of advanced prostate cancer. But men with high intake of omega-3 fatty acids had a substantially reduced risk, even if they carried the COX-2 variant.

Age Related Macular Degeneration
In the US Twin Study of Age Related Macular Degeneration, fish consumption and dietary omega-3 fatty intake was inversely associated with age related macular degeneration.

In individuals with early or intermediate stages of age related macular degeneration, total and specific types of fat intake, as well as some fat-containing food groups, modifies the risk of progression to advanced age related macular degeneration while fish intake and nuts reduces risk of advanced age related macular degeneration.

In a multicenter eye disease case-control study involving 349 individuals (age range, 55-80 years) with advanced age related macular degeneration and 504 control subjects without age related macular degeneration, but with other ocular diseases, higher dietary intake of omega-3 fatty acids was associated with a lower risk for age related macular degeneration among individuals consuming diets low in linoleic acid, an omega-6 fatty acid.