The Health Implications of Vitamin D Insufficiency and Low Energy Availability in Athletes

Review Article

Austin J Nutr Metab. 2016; 3(1): 1034.

The Health Implications of Vitamin D Insufficiency and Low Energy Availability in Athletes

Arlinghaus K, Ruckstuhl K and Cialdella-Kam L*

Department of Nutrition, Case Western Reserve University, USA

*Corresponding author: Lynn Cialdella-Kam, Department of Nutrition, Case Western Reserve University, School of Medicine-WG 48, 10900 Euclid Avenue, Cleveland, OH 44106, USA

Received: May 28, 2016; Accepted: July 27, 2016; Published: July 29, 2016


Vitamin D and its extraskeletal effects has been the subject of recent research in the general population, but in the athletic community, research is scarce. In athletes, vitamin D may help to reduce infections and illnesses and improve muscle health. In this review article, we examined vitamin D insufficiency in the context of athletes with low energy availability (EA), defined as dietary energy intake (EI; kcal/day) less exercise energy expenditure (EEE; kcal/day). In female athletes, EA is considered optimal at >45 kcal/kg of fat free mass (FFM)/ day and associated with menstrual disturbances at ~30 kcal/kg of FFM/day. Adverse health outcomes in female athletes have been associated with low EA including hormonal alterations, abnormal menses, and compromised immune function and musculoskeletal health. Research is limited in male athletes with low EA, but similar health concerns have been reported. To treat low EA in athletes, current guidelines include increasing EI (e.g., inclusion of energy dense foods) or decreasing EEE (e.g., including a day off from training) and ensuring adequate intake of the bone building nutrients, calcium and vitamin D (i.e., meet the recommended dietary allowance (RDA) of 1,000 mg/day and 600 IU/day, respectively). Given vitamin D’s role as an immunomodulator and potential ergogenic aid for skeletal muscle, higher intakes of vitamin D (i.e., >RDA) may be justified as a preventive measure against injuries and illnesses typically associated with low EA; however, further research is warranted.

Keywords: Cytokines; Inflammation; Immune function; Muscle health; Sports performance


25(OH)D: 25-hydroxyvitamin D; AMP: Antimicrobial Protein Secretion; BMD: Bone Mineral Density; BSAP: Bone Specific Alkaline Phosphatase; EA: Energy Availability; EEE: Exercise Energy Expenditure; EI: Energy Intake; EAR: Estimated Average Requirement; IFN-γ: Interferon-γ; IL: Interleukin; IgM: Immunoglobulin M; IGF- 1: Insulin-like Growth Factor-1; NTx: N-telopeptide; SIgA: Secretory Immunoglobulin A; Th: T helper; TNF-α: Tumor Necrosis Factor-α; RDA: Recommended Dietary Allowance; RED-S: Relative Energy Deficiency in Sport; URTI: Upper Respiratory Tract Infections; UV: Ultraviolet; VDBP: Vitamin D-binding Protein; WBC: White Blood Cell


Vitamin D, a key bone nutrient, has been implicated in a variety of domains important to athletic performance including immune function, inflammatory responses, and skeletal muscle function [1,2]. However, only ~44% of athletes have been reported to meet their vitamin D needs based on serum 25-hydroxyvitamin D (25(OH) D) levels [3]. Vitamin D levels are considered to be deficient in athletes if serum 25(OH)D levels are <50 nmol/L (20 ng/mL) and insufficient if levels are between 50 and 75 nmol/L (20-30 ng/mL) [4]. As with the general population, athletes should strive to meet the recommended dietary allowance (RDA) for vitamin D of 600 IU/ day [4,5]. Sun exposure is the primary form of obtaining vitamin D given that dietary sources are limited [6]. Ultraviolet (UV) B rays penetrate the skin, and provitamin D3 (7-dehydrocholesterol) is converted into previtamin D3 as a result [6]. The body’s heat then causes isomerization of this compound into cholecalciferol (vitamin D3), which is further converted into 25(OH)D in the liver and finally into the active form, 1,25(OH) vitamin D, in the kidney [6]. However, regular sun exposure may be limited for a variety of reasons including living in high latitude, adhering to skin cancer prevention guidelines, training primarily indoors, and wearing clothing that covers skin for religious reasons [2,7]. In general, athletes who participate in outdoor sports (e.g., tennis, soccer, cross country, track and field, football, and cycling) have been shown to have higher 25(OH)D levels when compared to those who train indoors (e.g., swimming, basketball, dancing, gymnastics, volleyball, and wrestling) [3,8- 12]. Therefore, vitamin D must be obtained from fortified foods and dietary supplements. Dietary sources and supplements provide vitamin D either as ergocalciferol (vitamin D2) or cholecalciferol (vitamin D3) [13], which is absorbed from the intestine into the bloodstream via chylomicrons [6]. In circulation, vitamin D binds to vitamin D-binding protein (VDBP) and is transported to the liver where it is converted to 25(OH)D and then to 1,25(OH)D in the kidney [6]. In both synthesis pathways, the active form, 1,25(OH)D, is responsible for the associated roles of vitamin D such as immune and musculoskeletal health [13].

Vitamin D is a particularly important micronutrient for female athletes with low energy availability (EA) [14]. EA refers to the calories remaining after exercise (i.e., dietary energy intake (EI; kcal/day) less exercise energy expenditure (EEE; kcal/day)) for daily living activities and metabolic processes [14]. Females with an EA of <45 kcal/kg of fat free mass (FFM) per day are considered to have suboptimal EA and are at an increased risk for stress fractures, musculoskeletal injuries, and immunosuppression [14]. Furthermore, low EA has been associated with menstrual dysfunction at levels of ~30 kcal/ kg of FFM per day based on energy restriction studies conducted in sedentary women [15,16]. However, EA assessment requires accurate measurements of both EI and EEE [17]. In addition, adverse health consequences such as menstrual dysfunction occur in some women with EA >30 kcal/kg of FFM per day [18]. Females have primarily been the focus of low EA, particularly with regard to the female athlete triad, which describes the interrelationship among EA, bone health, and menstrual function [14]. Relative Energy Deficiency in Sport (RED-S) was recently introduced with the goal of including both female and male athletes and recognizes a diverse array of health and performance effects associated with low EA [19]. Such effects extend beyond the previously recognized components of the female athlete triad and include disruptions in metabolic rate, immunity, protein synthesis and cardiovascular health [19]. The purpose of this review article is to describe the health and sports performance implications of vitamin D insufficiency in the context of athletes with low EA.

Low energy availability and vitamin D

Athletes in sports in which low body fat confers a competitive advantage such as running, cycling, and gymnastics are at increased risk for low EA [4]. In female athletes, low EA has been linked to poor bone health, menstrual dysfunction, hormonal disruptions (i.e., low thyroid, insulin-like growth factor-1 (IGF-1), and leptin levels, and high cortisol levels), compromised immune function, and increased risk of musculoskeletal injuries [14,19]. Key nutrition interventions include improving EA by increasing EI (e.g., energy dense snacks) or decreasing EEE (e.g., incorporating a day off from training) and by ensuring that athletes meet the RDA for the key bone nutrients, calcium and vitamin D [18-21]. To our knowledge, no studies have examined whether athletes with low EA have a higher prevalence of vitamin D insufficiency compared to normal controls, but a few studies have reported dietary intake and circulating 25(OH)D levels in athletes with low EA or EI [18,22,23]. Viner, et al. (2015) assessed dietary intake via 3-day food logs male and female cyclists (n=10), 70% of whom were classified as having low EA (defined as < 30 kcal/ kg FFM/day) across the season. All cyclists were reported to have inadequate food intake of vitamin D (i.e., < RDA). Although, 90% of the cyclists reported taking calcium (500-1,000 mg/day) and vitamin D supplements (400-5,000 IU/day) due to insufficiencies [23]. In a 6-month carbohydrate-protein intervention in endurance-trained female athletes (8 with exercise-induced menstrual dysfunction and 9 eumenorrheic controls), Cialdella-Kam, et al. (2014) reported that slightly over half had dietary vitamin D intakes less than the Estimated Average Requirement (EAR) of 400 IU/day as determined by analysis of 7-day weighed food records. Only 3 individuals with menstrual dysfunction had low EA (<30 kcal/kg FFM/day) and mean EA was similar in eumenorrheic and oligo/amenorrheic athletes (~37-38 kcal/ kg FFM/day) [18]. All participants, including the three individuals with low EA and menstrual dysfunction, had adequate blood levels of 25(OH)D (average levels=~105 nmol/L) with 40% reporting using a vitamin/mineral supplement [18]. In adolescent female cross country runners (n=39), Barrack, et al. (2010) examined the relationship among energy deficiency (defined as <2000 kcal/day), elevated bone turnover, and vitamin D levels. Runners with elevated bone turnover exhibited a profile of energy deficiency and had lower serum 25(OH)D levels (n=13; mean=80.6 nmol/L) compared to those with normal bone turnover (n=26, mean=91.6 nmol/L) [22]. Prevalence of inadequate dietary vitamin D intake (<RDA) was similar for both groups (39% and 46% for normal and elevated bone turnover groups, respectively) [22]. Based on these few studies, vitamin D insufficiency does not appear to be more prevalent in those with low EA vs. normal controls, but further research in this area is warranted. Moreover, low EA has been associated with decreased bone mineral density (BMD) and increased risk of stress fractures [14]. Athletes are classified as vitamin D deficienct at serum 25 (OH)D levels between 50-70 nmol/L; however, higher serum 25(OH)D levels (i.e., up to 125 nmol/L) have been proposed to prevent stress fractures and to optimize adaptations from training [4,24,25]. In addition, intensive exercise training and/ or low EA can lead to chronic stress, inflammation, and impaired immunity and musculoskeletal health (Figure 1) [26-28]. As discussed below, vitamin D is involved in immunomodulation and possibly helps to maintain skeletal muscle health [1,2,29]. Thus, higher levels of vitamin D (>RDA) may be warranted in athletes with low energy availability to protect against injuries and illnesses and to optimize sports performance [4,24,25,29].

Citation: Arlinghaus K, Ruckstuhl K and Cialdella-Kam L. The Health Implications of Vitamin D Insufficiency and Low Energy Availability in Athletes. Austin J Nutr Metab. 2016; 3(1): 1034.