A measurable substance in an organism that is indicative of some phenomenon such as disease, infection, or environmental exposure.

Any of a group of complex proteins or conjugated proteins that are produced by living cells and act as catalyst in specific biochemical reactions.

A type of water-soluble B-vitamin, also called vitamin B9. Folate is critical in the metabolism of nucleic acid precursors and several amino acids, as well as in methylation reactions. Severe deficiency in folate can cause megaloblastic anemia, which causes fatigue, weakness, and shortness of breath. Certain genetic variations in folate metabolism, particularly those found in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene influences folate status. Inadequate folate status during early pregnancy increases the risk of certain birth defects called neural tube defects, or NTDs, such as spina bifida, anencephaly, and other similar conditions. Folate deficiency and elevated concentrations of homocysteine in the blood are associated with increased risk of cardiovascular disease. Low folate status and/or high homocysteine concentrations are associated with cognitive dysfunction in aging (from mild impairments to dementia). The synthetic form of folate is called folic acid. Sources of folate include most fruits and vegetables, especially green leafy vegetables.

The genetic constitution of an individual organism. The combination of genotype and environment determine an organism's physical characteristics – known as the phenotype.

An amino acid present in the blood. Homocysteine is produced during the metabolism of methionine. Abnormalities in methionine metabolism can lead to elevated homocysteine levels, a condition called hyperhomocysteinemia. Elevated homocysteine levels can contribute to arterial plaque formation and increase the risk of clot formation. Some evidence suggests that elevated homocysteine levels double the risk of developing Alzheimer’s disease. Homocysteine levels vary according to dietary intake, with highest levels associated with consumption of animal protein. Variants in the genes that encode for the enzymes that metabolize homocysteine, specifically MTHFR, or methylenetetrahydrofolate reductase, markedly increase the risk of developing a wide array of diseases, including cardiovascular disease, Alzheimer’s disease, and cancer. High intake of dietary folate (present in leafy greens and other fruits and vegetables) can modulate the harmful effects associated with MTHFR.

A gene coding for an enzyme that converts homocysteine into methionine; a critical step in the methyl cycle. Natural variation in this gene is common among healthy people, however, some variants have been reported to influence susceptibility to occlusive vascular disease, neural tube defects, Alzheimer’s disease and other forms of dementia, colon cancer, and acute leukemia.

A study in which people are randomly allocated to receive one of several clinical interventions. One of these interventions is the standard of comparison or control. The control may be a standard practice, a placebo, or no intervention at all.

A change in one nucleotide DNA sequence in a gene that may or may not alter the function of the gene. SNPs, commonly called "snips," can affect phenotype such as hair and eye color, but they can also affect a person's disease risk, absorption and metabolism of nutrients, and much more. SNPs differ from mutations in terms of their frequency within a population: SNPs are detectable in >1 percent of the population, while mutations are detectable in <1 percent.