Upper level folate

Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its Panel on Folate, other B vitamins, and Choline and Subcommittee on Upper Reference Levels of Nutrients. Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. Washington DC National Academy Press, 1998. 

A study of 1401 subjects involved measuring plasma homocysteine and measuring the lesions in the carotid artery, one of the arteries in the body that tends to acquire atherosclerotic lesions. The thickness of the lesions were measured by ultrasonography. Plasma folate, vitamin Bg, and vitamin B12 were also measured. A correlation was found between narrowing of the artery and homocysteine levels at above 15 xM homocysteine. A correlation with narrowing of the artery was also found with folate levels below 2.5 ng/ml, and with vitamin Bg levels below 30 nM (Selhub et al, 1995). A study of 231 normal subjects and 304 patients with atherosclerosis (coronary artery under 30% normal diameter) revealed a striking correlation between plasma homocysteine of 12 pM, or greater, and atherosclerosis (Robinson et al, 1995). These studies help define an upper limit of acceptable plasma homocysteine levels. 

Sources Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Huoride (1997) Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin 85, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline (1998) EHetary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (2000) Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001) Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005) and EHetary Reference Intakes for Calcium and Vitamin D (2011). These reports may be accessed via www.nap.edu A Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects to almost all individuals in the general population. Unless otherwise specified, the UL represents total intake from food, water, and supplements. Due to a lack of suitable data, ULs could not be established for vitamin K, thiamin, riboflavin, vitamin B12, pantothenic acid, biotin, and carotenoids. In the absence of a UL, extra caution may be warranted in consuming levels above recommended intakes. Members of the general population should be advised not to routinely exceed the UL. The UL is not meant to ply to individuals who are treated with the nutrient under medical supervision or to individuals with predisposing conditions that modify their sensitivity to the nutrient... 

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