Vitamin D Deficiency

According to the Australian Institute of Sport (National Health and Medical Research Council, 2005), while there is currently no universal definition of vitamin D deficiency, the most commonly used definitions in scientific and clinical literature, based on blood plasma concentration of the metabolite 25(OH)D (Table 67), are:

Deficiency: < 20 ng/ml (50 nmol/l);
Insufficiency: < 30 ng/ml (less than 75 nmol/l);
Satisfactory level: > 30 ng/ml (75 nmol/l and above);
Ideal range*: 75‒120 nmol/l;
Toxic level: >375 nmol/l.

These levels are considered along with increased concentrations of ionized calcium in the blood serum. The upper limits of this range are preferred for maintaining high physical readiness in elite athletes and are safe.

However, many scientific sports organizations, such as the Gatorade Sports Science Institute in Liverpool, UK, believe that these recommendations cannot be universal due to the variability of vitamin D levels in different countries and regions. A differentiated approach should consider not only the country as a whole but also its individual regions, as well as factors like the time of year, gender, age of athletes, and other factors. Such an approach enables proper correction of deficiency or insufficiency (dosage, duration of treatment) and the integration of these results into the broader practice of sports medicine as part of the overall National Athlete Preparation Program.

Classification of Deficiency, Insufficiency, and Optimal Levels of Vitamin D

Classification of Deficiency, Insufficiency, and Optimal Levels of Vitamin D (according to various international professional expert organizations):

Organization Name	Vitamin D Deficiency	Vitamin D Insufficiency	Sufficient Vitamin D Content
U.S. Institute of Medicine	<12 ng/ml (<30 nmol/l)	12–20 ng/ml (30–50 nmol/l)	≥20 ng/ml (≥50 nmol/l)
International Endocrine Society, 2011	<20 ng/ml (<50 nmol/l)	21–29 ng/ml (51–74 nmol/l)	≥30 ng/ml (≥75 nmol/l)
Swiss Federal Nutrition Commission	<20 ng/ml (<50 nmol/l)	21–29 ng/ml (51–74 nmol/l)	≥30 ng/ml (≥75 nmol/l)
Spanish Society for Bone and Mineral Research	<20 ng/ml (<50 nmol/l)	21–29 ng/ml (51–74 nmol/l)	≥30 ng/ml (≥75 nmol/l)
European Society for Clinical and Economic Aspects of Osteoporosis	<10 ng/ml (<25 nmol/l)	<20 ng/ml (<50 nmol/l)	20–30 ng/ml (50–75 nmol/l)
UK National Osteoporosis Society	<12 ng/ml (<30 nmol/l)	12–20 ng/ml (30–50 nmol/l)	>20 ng/ml (>50 nmol/l)

Vitamin D Metabolism in the Body

There are two natural forms of vitamin D: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is available in limited quantities from plant sources and in some dietary supplements and medications, while vitamin D3 is obtained from fish oils and dairy products. However, the primary source of vitamin D3, accounting for 90% of intake, is synthesis in the skin through photosynthesis when exposed to sufficient sunlight. Regardless of the source, 99% of vitamin D binds to specific proteins (vitamin D-binding protein — DBP), while the remainder binds to albumin.

Both forms of vitamin D undergo hydroxylation, first in the liver (catalyzed by 25-hydroxylase to the metabolite 25-hydroxyvitamin D [25(OH)D]), and then in the kidneys (catalyzed by 1-α-hydroxylase to the biologically active form of vitamin D — 1-α,25-dihydroxyvitamin D3 [1-α,25(OH)D]). This active form interacts with vitamin D receptors (VDR) in cells, which are located in all tissues of the body, and then decodes inside the cell and binds to vitamin D-responsive elements (VDREs) in the DNA. In the absence of such interaction, VDREs undergo degradation, resulting in an inactive form (Close G.L., 2015).

Prevention of Vitamin D Deficiency: 1.1 Recommended supplements for the prevention of vitamin D deficiency are cholecalciferol (D3) and ergocalciferol (D2). (Evidence level B I).

1.2 Individuals aged 18–50 years are advised to consume at least 600–800 IU of vitamin D daily for prevention. (Evidence level B I).

1.3 Individuals over 50 years are advised to

consume at least 800–1000 IU of vitamin D daily for prevention. (Evidence level B I).

1.4 Pregnant and breastfeeding women are recommended to consume at least 800–1200 IU of vitamin D daily for prevention. (Evidence level B I).

1.5 To maintain a 25(OH)D level of over 30 ng/ml, a daily intake of at least 1500–2000 IU of vitamin D may be required. (Evidence level A I).

1.6 In diseases/conditions accompanied by impaired absorption/metabolism of vitamin D, it is recommended to take doses of vitamin D 2–3 times higher than the daily requirement for the age group. (Evidence level B I).

1.7 Without medical supervision and monitoring of 25(OH)D blood levels, it is not recommended to prescribe vitamin D doses exceeding 10,000 IU per day for an extended period (more than 6 months). (Evidence level B I).

*Note: The recommended reference interval for laboratories is 30–100 ng/ml (75–250 nmol/l).

Classification of Deficiency, Insufficiency, and Optimal Levels of Vitamin D

Vitamin D Metabolism in the Body

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Vitamin D Deficiency

Classification of Deficiency, Insufficiency, and Optimal Levels of Vitamin D

Vitamin D Metabolism in the Body

Retina and Peptides — Analytical Review

Adrenoprotective Effects of the Peptide IPH LGA

Maximizing Your Workout: The Benefits of BCAA with Peptides

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