Every 10-nmol increase in levels of 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form of the vitamin) was associated with a 0.03-kbp longer telomere in leukocytes in middle-aged adults, according to data extracted from the National Health and Nutrition Examination Survey (NHANES) 2001–2002.

The findings, published in the Journal of Nutrition​​,​ show correlation and not causation, but could have implications for our understanding of healthy aging and potential cancer risk reduction.

However, “[t]he actual clinical impact of our findings requires further investigation,”​ wrote the researchers from Harvard Medical School, Harvard T.H. Chan School of Public Health, the University of Tromsoe–The Arctic University of Norway, and University Hospital of North Norway.

Telomeres​

The aging and lifespan of normal, healthy cells are linked to the so-called telomerase shortening mechanism, which limits cells to a fixed number of divisions. During cell replication, the telomeres function by ensuring the cell's chromosomes do not fuse with each other or rearrange, which can lead to cancer. Elizabeth Blackburn, a telomere pioneer at the University of California San Francisco, likened telomeres to the ends of shoelaces, without which the lace would unravel.

With each replication the telomeres shorten, and when the telomeres are totally consumed, the cells are destroyed (apoptosis). Previous studies have also reported that telomeres are highly susceptible to oxidative stress and inflammation. Some experts have noted that telomere length may be a marker of biological aging.

“LTL [leukocyte telomere length] is recognized as a measure of a cell’s replication and its remaining proliferative potential,” ​explained the authors of the new paper. “Age is a well-established factor associated with telomere shortening.​

“[M]odifiable conditions and factors such as poor diet, being overweight or obese, and sedentary lifestyle—which are highly correlated with inflammation—are also associated with telomere shortening,” ​they added.

Study details​

version="1.0" encoding="utf-8"? Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25(OH)D, the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D). Image © iStock/CharlieAJA

The scientists analyzed data from 1,542 younger adults aged between 20 and 39, 1,336 middle-aged adults aged between 40 and 59, and 1,382 adults 60 and over.

After adjusting the numbers to account for potentially confounders such as gender, race/ethnicity, BMI, and other factors, the researchers found that 25(OH)D levels of at least 50 nmol/L were associated with 0.13-kbp longer LTL in middle-aged adults with, compared with the same aged adults with 25(OH)D levels less than 50 nmol/L.

Potential role for cancer risk reduction​

The results also presented a potential mechanism of action for the reported anti-cancer effects of vitamin D, which were first proposed in 1941 when Frank Apperly​ demonstrated a link between latitude and deaths from cancer, and suggested that sunlight gave "a relative cancer immunity".

Since then there have been numerous studies suggesting associations between vitamin D and lower risks of certain cancers.

“Because malignancy can be a consequence of genomic instability and telomere shortening, our findings of a positive association between serum 25(OH)D and LTL could be interpreted as a possible mechanism for the ‘protective role’ of vitamin D and as a justification for further RCTs with cancer as a primary outcome,” ​wrote Beilfuss et al.

Source: Journal of Nutrition​​

Published online ahead of print, doi:10.3945/jn.116.244137

“Serum 25-Hydroxyvitamin D Has a Modest Positive Association with Leukocyte Telomere Length in Middle-Aged US Adults”​

Authors: J. Beilfuss et al.