What are the critical illness implications of micronutrient deficiency?

From the Guidelines

Micronutrient deficiencies should be addressed promptly in critically ill patients to improve outcomes, with supplementation including vitamins C, D, B1, zinc, and selenium, and monitoring of micronutrient levels when feasible, particularly for prolonged ICU stays. Critical illness increases metabolic demands while simultaneously reducing intake and absorption, creating a perfect storm for deficiency. Supplementation should include vitamins C (1-2g daily), D (cholecalciferol 50,000 IU weekly if deficient), B1 (thiamine 200-300mg daily for 3-5 days), zinc (20mg elemental zinc daily), and selenium (100-400mcg daily) 1. Early enteral nutrition is preferred when possible, as it helps maintain gut integrity and improves micronutrient absorption. For patients unable to tolerate enteral feeding, parenteral multivitamin preparations should be administered. Specific deficiencies may require targeted replacement: thiamine for alcoholic patients or those with refeeding syndrome, vitamin K for coagulopathy, and zinc for wound healing or diarrheal illness.

• Key micronutrients to monitor and supplement include:
  • Copper, due to its role in immune function and antioxidant defense
  • Selenium, due to its role in antioxidant defense and immune function
  • Zinc, due to its role in wound healing and immune function
  • Iron, due to its role in oxygen transport and energy production
• Laboratory monitoring of micronutrient levels is recommended when feasible, particularly for prolonged ICU stays, with testing initiated after 6-7 days in ICU 1.
• Micronutrients play crucial roles in immune function, antioxidant defense, wound healing, and metabolic processes, all of which are stressed during critical illness, and deficiencies can worsen outcomes by impairing these essential functions, while appropriate supplementation supports recovery and reduces complications 1.

From the Research

Micronutrient Deficiency in Critical Illness

• Micronutrients have essential antioxidant and immune functions, and low blood concentrations are frequently observed in critically ill patients 2.
• The concepts of complementation, repletion, or even pharmacological supplementation have been explored, but many clinical studies have yielded controversial or negative results 2.
• Current practices of micronutrient provision and monitoring in critical care vary substantially across the world, and low plasma/serum micronutrient levels do not always reflect a true deficiency in the absence of demonstrable losses 2, 3.

Essential Micronutrients in Critical Illness

• Numerous micronutrients are involved in antioxidant and immune defence, and their blood concentrations are frequently low in critically ill patients 3.
• Higher needs and deficiencies are frequent for some micronutrients, such as thiamine, vitamins C and D, selenium, zinc, and iron, and have been acknowledged with identifying patients at risk 3.
• Vitamin D blood levels less than 12 ng/ml are associated with poor clinical outcomes, and supplementation in deficient ICU patients generates favourable metabolic changes and decreases mortality 3.

Micronutrient Deficiencies and Critical Illness

• Low micronutrient levels in critical illness have been reported in multiple studies, and micronutrient deficiency may augment oxidative stress in critical illness 4.
• Micronutrient blood concentrations were found to be lower in ICU patients compared to healthy age-matched controls, and vitamin C levels dropped significantly during the first days of ICU admission 4.
• No association between micronutrient levels and severity of illness, C-reactive protein (CRP), or micronutrient intake was found 4.

Micronutrient Status Alterations in Critically Ill Patients

• Micronutrient status alterations are associated with several complications and worse outcomes in critically ill patients, and improving micronutrient status has been shown to be a potential co-adjuvant therapy 5.
• High-dose monotherapy of micronutrients is not recommended, and basal daily needs must be provided, with higher doses in diseases with known higher needs, and identified deficiencies treated 5.
• A rigorous rebalancing of research strategies and priorities is needed to improve clinical practice, and ongoing trials on micronutrients in critically ill patients have been identified 5.

Immune Support by Micronutrients

• Immune support by micronutrients is historically based on vitamin C deficiency and supplementation in scurvy, and it has since been established that the complex, integrated immune system needs multiple specific micronutrients 6.
• Adequate amounts of micronutrients are essential to ensure the proper function of physical barriers and immune cells, and daily micronutrient intakes necessary to support immune function may be higher than current recommended dietary allowances 6.
• Supplementation with multiple micronutrients with immune-supporting roles may modulate immune function and reduce the risk of infection, and micronutrients with the strongest evidence for immune support are vitamins C and D and zinc 6.