Study elucidates complex link between vitamin D and testosterone in obese men

The new research was published in the journal Frontiers in Endocrinology​.  It was the work of experts associated with a research hospital in Malaga, Spain and a research institute in Madrid.

The researchers recruited young  men being treated for obesity in Malaga in the years 2013 to 2015.  They excluded subjects diagnosed with any of the many comorbidities associated with obesity, such as type 2 diabetes, cardiovascular disease, etc.   They also excluded subjects who had been treated in such a way as to artificially alter the body’s vitamin D level.

Cohort subdivided by 25(OH)D level

They ended up with a cohort of 269 younger men, who for the purposes of statistical analysis were divided into two groups: those with 25-hydroxyvitamin D—or 25(OH)D—levels of 20 ng/Ml or more and those who fell below.  A level of 20 ng/Ml 25(OH)D has been defined as the minimal healthy level by the US Institutes of Medicine, with a maximal healthy value pegged at 50 ng/Ml.

The younger men ranged in age from early 30s to the mid 40s, and from moderately to morbidly obese. The average BMI in the vitamin D sufficiency group was about 37 with in the insufficiency group it landed at almost 41. Around a quarter of both groups were active tobacco smokers.

The researchers noted that low testosterone is a well known side effect of obesity. The also said that some studies have uncovered an association with low vitamin D levels and low testosterone in these groups, but the mechanism remained unclear.

“Only a few studies have investigated the effect of vitamin D on testosterone levels in the context of obesity, despite the previously mentioned data that strongly suggested a feasible relationship. Therefore, the aim of the present study was to investigate the relationship between serum 25(OH)D and testosterone levels in young men with different grades of obesity. We hypothesized that a low serum 25(OH)D levels in obese men would be associated with lower testosterone levels,” ​the researchers wrote.

The study divided the two groups up into three subgroups each, which the researchers dubbed Types I, II and III. These were defined as BMI of between 30 and 35, 35 to 40 and the final group having a BMI of 40 or greater, which qualifies as morbidly obese.

Also, to further elucidate the relationship of vitamin D levels to the endocrine status of the men, the researchers assessed the levels of an array of sex-related factors beyond testosterone. They included the hormones androstenedione and estradiol, SBGH (sex hormone binding globulin) and other factors.

Complex relationship

When correcting for both the various levels of obesity among the cohort and their smoking status, the researchers found the correlation between vitamin D status and low testosterone was more nuanced that might be concluded from earlier research.  There is a weak correlation running through the entire cohort, but it only reached clinical significance for one group, suggesting that more work needs to be done to fully understand the relationship.

“When different grades of obesity were examined, serum 25(OH)D levels were found to be related to total testosterone and SHBG levels in participants with morbid obesity, suggesting that vitamin D may have specific benefits in those subjects with very low testosterone levels and severe cases of obesity. Additional research is needed to elucidate possible common mechanisms,”​ they said.

Source: ​Frontiers in Endocrinology​
doi.org/10.3389/fendo.2022.960222​
25-hydroxyvitamin D and testosterone levels association through body mass index: A cross-sectional study of young men with obesity​
Authors: Damas-Fuentes M, et al.