Table 1.

Key messages, practical considerations and important education messages on energy, vitamin D, iron and hydration for the youth winter sport athlete.

Energy	Importance for the youth winter sports athlete:
	• Sufficient energy availability is essential for optimal growth, maturation, and sporting performance (>45 kcal−1 · kg FFM−1·day−1 for adults).
	Practical considerations and application:
	• The energy requirements of youth winter sport athletes vary considerably. Consider each athlete's anthropometric profile, rate of growth, NEAT, and sporting demands (including training and competition load).
	• Monitor rate of growth (stature and body mass) and maturation (maturity offset, i.e., time from PHV)-3–4 times per year.
	• Be alert to any symptoms of low energy availability (RED-S) such as chronic fatigue sensation, low mood, reduced performance, poor concentration, impaired immune system and in females, absence of menarche.
	Education:
	• Energy density and macro-/micronutrient content of different foods.
	• Weighing out and visualizing a “typical day's food.”
	• Importance of not missing meals and snacks.
	• Planning nutrition into their schedule (e.g., when traveling or at school).
Vitamin D	Importance for the youth winter sports athlete:
	• Winter sports athletes are at risk of vitamin D deficiency. This prohormone, alongside calcium, is required in sufficient quantities for bone mineral accrual to ensure optimal skeletal growth and development.
	Practical considerations and application:
	• Assess vitamin D status and supplement vitamin D3 accordingly. Vitamin D status can be obtained via a simple finger prick blood sample (and appropriate analysis), or regular blood lab analysis.
	• If unable to determine vitamin D status a safe dose (typically 800 IU per day−5600 IU per week) may be beneficial to prevent deficiency during winter months.
	• Consider ethnicity, habitual latitude, and frequency of skin exposure to sunlight.
	Education:
	• Difficult to be obtained in sufficient amounts through diet.
	• Importance of (safe) sunlight exposure.
	• Need for correcting a deficiency through safe sunlight exposure and/or supplementation.
Iron	Importance for the youth winter sports athlete:
	• Iron is an important mineral for many biological processes. Iron requirements increase as a result of (tissue) growth and in females increase further due to menarche.
	Practical considerations and application:
	• High prevalence of iron deficiency in youth athletes due to insufficient dietary iron intake.
	• Iron requirements may be increased at altitude, which is relevant for altitude training camps.
	• Non-haem iron (primarily from non-animal sources) has a low bioavailability making vegetarian/vegan athletes at greater risk of iron deficiency.
	• Iron absorption is enhanced when consumed with vitamin C and is impaired when consumed alongside tea and coffee.
	• In case of deficiency iron supplementation should be prescribed by a qualified clinical practitioner.
	Education:
	• Iron rich foods and their bioavailability.
	• Food items and combinations that inhibit or favor iron uptake.
	• Symptoms of iron deficiency (e.g., unexplained fatigue sensation, loss of concentration, diminished performance).
Hydration	Importance for the youth winter sports athlete:
	• There are differences in thermoregulation mechanisms between adult and youth athletes, and among adolescents depending on maturation state. Furthermore, differences in environment, clothing, and metabolic demands between sports lead to differences in heat dissipation and subsequent fluid requirements.
	Practical considerations and application:
	• Consider environment (i.e., temperature, humidity, and altitude) in addition to clothing.
	• Appropriate fluid availability (whilst considering environmental temperature) during training and competition, ensuring enough fluids are consumed to prevent excessive dehydration (i.e., >2% of body mass).
	• Add flavorings and use hot or cold drinks when appropriate to increase palatability and consumption.
	• Check urine color (aim for pale colored urine).
	• Check body weight pre- and post-training session/competition to assess fluid losses and determine optimal drinking strategy (including rehydration at 1.5 L fluids per kg body mass lost).
	Education:
	• Urine color charts to illustrate hydration/dehydration.
	• Individualized fluid loss assessment.
	• Optimal drinking scheme for the specific sport.

NEAT, non-exercise activity thermogenesis; RED-S, relative energy deficiency in sport; PHV, peak height velocity. Please see main text for references.