Micronutrient deficiencies in critical illness

Low micronutrient levels in critical illness have been reported in multiple studies. Because of the antioxidant properties of various micronutrients, micronutrient deficiency may augment oxidative stress in critical illness. However, it remains unclear whether micronutrient concentrations in ICU patients are different from those in healthy age-matched controls. It is also unclear whether micronutrient deficiency develops, worsens, or resolves during ICU admission without supplementation.

We prospectively studied a cohort of adult critically ill patients. Micronutrient levels, including selenium, β-carotene, vitamin C, E, B₁ and B₆ were measured repeatedly during the first week of ICU admission. We compared the micronutrient concentrations at ICU admission to those of healthy age-matched controls. In addition, associations between micronutrient concentrations with severity of illness, inflammation and micronutrient intake were investigated.

Micronutrient blood concentrations were obtained from 24 critically ill adults and 21 age-matched healthy controls. The mean micronutrient levels at admission in the ICU patients were: selenium 0.52 μmol/l, β-carotene 0.17 μmol/l, vitamin C 21.5 μmol/l, vitamin E 20.3 μmol/l, vitamin B₁ 129.5 nmol/l and vitamin B₆ 41.0 nmol/l. In the healthy controls micronutrient levels of selenium (0.90 μmol/l), β-carotene (0.50 μmol/l), vitamin C (45 μmol/l) and vitamin E (35.5 μmol/l) were significantly higher, while vitamin B₁ (122 nmol/l) and B₆ (44 nmol/l) were not significantly different between patients and controls. Selenium, vitamin B₁ and vitamin B₆ levels remained stable during ICU admission. Vitamin C levels dropped significantly until day 5 (p < 0.01). Vitamin E and β-carotene levels increased significantly on days 5-7 and day 7, respectively (p < 0.01). Micronutrient levels were not associated with severity of illness, CRP or micronutrient intake during the admission.

At admission, ICU patients already had lower plasma levels of selenium, β-carotene, vitamin C and vitamin E than healthy controls. Vitamin C levels dropped significantly during the first days of ICU admission, while β-carotene and vitamin E levels increased after 5-7 days. No association between micronutrient levels and severity of illness, C-reactive protein (CRP) or micronutrient intake was found. Progressive enteral tube feeding containing vitamins and trace elements does not normalize plasma levels in the first week of ICU stay. This was a hypothesis generating study and more investigation in a larger more diverse sample is needed.