In a recent study published within the Journal Nutrients, researchers investigated the consequences of vitamin D/iron statuses and calcium intake on lumbar cortical and trabecular bone in male adults aged 15-19.

Study: The Relationship between Bone Health Parameters, Vitamin D and Iron Status, and Dietary Calcium Intake in Young Males. Image Credit: Tatjana Baibakova/Shutterstock.com

Background

There are several knowledge gaps in research on the consequences of nutrients on bones. First, research has focused only on the cortical a part of the bones or their metabolism, not the trabecular. 

Second, the outcomes from studies (most done using animal models) investigating the consequences of micronutrients, as an example, vitamin D, on trabecular bone structure should be clarified.

Third, the little research done on human subjects has focused on the elderly population, which is why it stays obscured how the provision of some nutrients is important for maintaining a healthy skeleton in adults and for bone growth and development across childhood.

One other challenge with research on the exclusive effects of vitamin D on bone health is that almost all have relied on computed measures of a complete of 25(OH)D in serum as an alternative of the free fraction of 25(OH)D; the latter is a superior measure of vitamin D status for bone health. 

Moreover, despite evidence of a cause-and-effect relationship between vitamin D (with calcium) and the chance of low-trauma bone fractures, the connection between vitamin D status and bone mineral density (BMD) stays ambiguous.

Finally, data on the association between iron deficiency (ID) and bone health are limited.

In regards to the study

In the current study, researchers analyzed data from 113 young male subjects who met the next criteria: i) aged between 15-19; ii) engaged in some osteogenic sports (volleyball or ski jumping) or were non-athletes (constituted the control group); iii) didn’t suffer from any injury across the 12 months before the study; iv) had body mass index (BMI) below 15 kg/m² and above 37 kg/m²; and v) provided informed consent.

Of those 113 participants, 76 were from Polish national youth ski jumping and volleyball teams (28 ski jumpers, 48 volleyball players), and 37 were non-athletes.

The team obtained the bone densitometry, lumbar spine bone mineral apparent density (BMAD), and trabecular bone rating (TBS) measurements using dual-energy X-ray absorptiometry (DXA).

Moreover, they evaluated body iron stores (Fe_S) based on serum ferritin and soluble transferrin receptor (sTfR) levels.

Moreover, they determined each participant’s dietary calcium intake using a semi-quantitative food frequency questionnaire.

Results

The outcomes confirmed a positive relationship between BMAD and Z-score and the vitamin D serum levels, with the association being stronger for the free fraction 25 (OH) D than the commonly used total fraction.

Free 25(OH)D explained 25% of the whole 32% of BMAD variation within the lumbar spine measurements of the sports group.

It’s noteworthy here that the free fraction constitutes only 0.1–2% of the whole hydroxy vitamin D within the human body, while the remaining circulates within the blood sure to albumin and mainly with vitamin D-binding proteins (VDBPs), implying, no less than theoretically, that the connection between each needs to be comparable across all individuals.

Nevertheless, on this study, the correlation between these two fractions within the athletes was lower than controls (0.77 vs. 0.93). Due to this fact, the authors presumed that physical exertion affects the whole hydroxy vitamin D fraction by influencing the VDBP levels.

Further, the authors noted that 22% and 15% of the athletes and controls, respectively, were iron-deficient.

While their ferritin and iron stores concurrently correlated with BMAD, no such correlation emerged with the Z-score within the sports group, which, to some extent, was attributable to the shortage of adjustment of the Z-score to height.

Of the whole 32% of BMAD variation observed within the lumbar spine measurements of the sports group, 7% was explained by ferritin, suggesting it’s a more reliable indicator of bone mineralization in athletes than the calculated iron stores.

Moreover, the standard calcium intake didn’t impact BMAD in each groups. Because the observed total fraction of 25(OH)D was low in each groups, it could have modulated calcium absorption within the gut.

During puberty, high calcium retention efficiency likely compensates for low calcium intake.

Nevertheless, prolonged vitamin D deficiency (even moderate) in maturity may severely impair dietary calcium absorption within the gut, leading to increased bone loss.

The authors found no relationship between the dietary aspects analyzed on this study and the trabecular structure of bones.

Though each BMAD and Z-score correlated with the TBS within the controls, the correlation coefficients differed, while no such correlation existed within the sports group.

Furthermore, the “Fractures” factor was comparable in examined groups and independent of mineralization and TBS within the lumbar spine, suggesting that it might be independent of the extent of physical activity and associated overloads.

Conclusions

The outcomes of the current study confirmed the positive influence of normal vitamin D and iron status on cortical bone status in physically energetic athletes.

Of their bone mineralization assessments, the free 25(OH)D fraction appeared as a greater indicator than the whole 25(OH)D and ferritin than calculated body iron stores.

Beyond dietary aspects, results suggested that their bone mineralization assessments needs to be adjusted-for-height BMAD, not raw aBMD data.

Moreover, in these athletes, osteogenic physical exercises (e.g., jumps) also possibly affect trabecular bone.