Two blood markers of liver health are aspartate aminotransaminase (AST) and alanine aminotransaminase (ALT). AST and ALT are proteins that are usually found inside liver cells, but when there is liver cell damage, they’re released into the blood. It’s important to note that these proteins can also be elevated in the blood because of muscle damage. The reference range for AST is 10-40 U/L, and 7-56 U/Lfor ALT, but are these values optimal for health and longevity?
In a meta-analysis that included ~9 million adults (average age, 51y) that were followed for up to 20 years, Kunutsor et al. (2014) reported the association between AST and ALT with all-cause mortality risk. For AST (4 studies, 9,046,609 subjects), 10-15 U/L was associated with maximally reduced all-cause mortality risk:
For ALT (8 studies, 9,087,436 subjects), 12-15 U/L was associated with maximally reduced all-cause mortality risk:
While these studies are relevant for middle-aged adults between ~50-70y, what about at older ages? Shown below are the AST and ALT values for adults older than 100 years (centenarians):
Interestingly, the centenarians’ AST and ALT values are not far from the meta-analysis data for middle-aged adults. For example, the centenarians’ AST values range from 17-23, and their ALT values from 9-14.
What are my my AST and ALT values? As shown below, I’ve measured them 9 times in the past 10 years. Based on the all-cause mortality and centenarian data my AST and ALT values are too high!
What am I doing to reduce my AST and ALT? Fructose is metabolized by the liver, where high amounts can increase liver cell damage, resulting in increased circulating AST and ALT (Le et al. 2009, Perez-Pozo et al. 2010). Therefore, I’ve reduced my total dietary fructose intake from ~16-18% during the 3 months prior to my last blood test (August, 2015), to ~11-14%. I plan on retesting within the next 2 months, to see if this approach works!
3/23/2016 Update: My average daily fructose intake, expressed as a percentage of total calories, for the 3-month period before my August 2015 blood test was 15.9%. During the 3-month period before my latest blood test (3/2016), my average daily fructose intake was 12.9%. Although a 3% decrease doesn’t seem like much, the difference between these 2 values is highly statistically significant (p value = 7.5E-12). Nonetheless, my liver enzymes didn’t change, with AST and ALT values of 28 and 30, respectively.
My next attempt to reduce my liver enzymes involves reducing my daily green tea intake. High doses of green tea have been shown to negatively affect the liver (Mazzanti et al. 2009). I currently drink ~6 cups of green tea per day, which may be too much. To test that hypothesis, I’ll reduce my daily green tea to 4 cups/day, and retest my liver enzymes in a few months. Stay tuned!
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