Before jumping into the data, it’s important to note that kidney function is commonly estimated (i.e. the estimated glomerular filtration rate, eGFR) with use of values for serum levels of creatinine, age, gender, and ethnicity.
Kidney function decreases during aging, from ~90 (thick black line) in young men (18-24y) to less than 70 mL/min/1.73 m^2 in men older than 75y (Baba et al. 2015):
Similarly, eGFR decreases in women, from values ~100 in youth to ~70 mL/min/1.73 m^2 in women older than 75y (Baba et al. 2015):
In both of the images above it’s important to note that the confidence interval includes the lowest 2.5% to 97.5% of the population, and is indicated by the dashed lines. Starting from the bottom, the lines correspond to the 2.5, 5, 25, 50 (median, dark black line), 75, 95, and 97.5 percentiles. For example, in young men, eGFR ranges from 75-130, whereas in men older than 75y, it ranges from 45-90 mL/min/1.73 m^2. In women, these values correspond to 70-138 in youth, and 48-95 mL/min/1.73 m^2 in women older than 75y.
Similar findings have been reported for the age-related decline in eGFR in other studies, including Wetzels et al. (2007). When comparing young adults (18-24 year olds) to older adults (> 85y), median eGFR values declined from ~95 to ~65 mL/min/1.73 m^2 in men, and from ~90 to ~60 mL/min/1.73 m^2 in women.
The importance of the age-related decline in eGFR is illustrated by an increased risk of death from all causes. As eGFR decreases from 90-150 mL/min/1.73 m^2, mortality risk increases (https://nccd.cdc.gov/CKD/detail.aspx?Qnum=Q629):
I’m not interested in any age-related declines in function, including my kidneys! What does my data look like? Shown below are 24 eGFR values since 2009. Note that from 2009-2013 (blue dots), I measured eGFR once per year. Over those 5 measurements, my average eGFR was 95 mL/min/1.73 m^2, and my age was 36-40 years. Based on the data of Baba et al. 2015, my kidney function was similar to the 18-24 year olds. In addition, my average eGFR value was better than what was reported for the 35-39 year olds, ~85 mL/min/1.73 m^2. So far so good!
In 2015, I started daily nutritional tracking, and measured my eGFR (and other variables) more often, up to 6x/yr. My average eGFR during that period is 100.1 mL/min/1.73 m^2. This value is close to being significantly higher than the pre-tracking (2009-2013) period (p-value = 0.057). My age range during that period was 42-46 years, and based on the Baba et al. 2015 data, is again similar to the median eGFR for the youngest reported group. Also, eGFR for the 40-49 yr olds, 78-80 mL/min/1.73 m^2, is again less than mine. It looks like I’ve avoided the age-related decline in kidney function (so far)!
Are there any dietary factors that may be affecting my eGFR? Interestingly, the strongest correlation (r = 0.42; R^2=0.18) is between my Vitamin A intake with eGFR:
My high daily Vitamin A intake is strongly correlated with my albumin levels (that info is in my book), with greater than 100,000 IU of Vitamin A being correlated with albumin levels ~5 mg/dL. However, based on the moderate negative correlation between Vitamin A with eGFR, it looks like I shouldn’t go higher than 100,000 IU of Vitamin A/day if I want to keep my eGFR ~100. Also note that because the correlation between Vitamin A with my eGFR is moderate (i.e. a correlation coefficient between 0.2 to 0.4) it may not be that at all, but something else. Stay tuned for more data!
If you’re interested, please have a look at my book!
Baba M, Shimbo T, Horio M, Ando M, Yasuda Y, Komatsu Y, Masuda K, Matsuo S, Maruyama S. Longitudinal Study of the Decline in Renal Function in Healthy Subjects. PLoS One. 2015 Jun 10;10(6):e0129036.
Wetzels JF, Kiemeney LA, Swinkels DW, Willems HL, den Heijer M. Age– and gender-specific reference values of estimated GFR in Caucasians: the Nijmegen Biomedical Study. Kidney Int. 2007 Sep;72(5):632-7.