**3.1 Indicators to assess vitamin A status**

 There are several indicators/biomarkers to detect VAD. The 'gold standard' method to assess vitamin A status is through the direct measurement of liver reserves of vitamin A through biopsy, since in human, vitamin A is stored abundantly (>90%) in the liver [22]**.** A study in average-weight individuals for 4 months had shown that an estimated cut-off at 0.07 μmol/g liver was able to protect them from any clinical signs of VAD [23]. Unfortunately, this method is not feasible for population evaluation [24, 25]. Therefore, other various methods are being proposed to assess and monitor VAD based on their different aspects. The two different ways include biological (clinical, functional, histological) and biochemical indicators [26]. In 2010, liver reserves of vitamin A were plotted against the commonly used indicators to define the range of liver reserves associated with the specific indicators. It was later updated in 2015 as presented in **Figure 1** [27].


#### **Figure 1.**

*The definition of vitamin A status assessed by using vitamin A indicators associated with vitamin A concentration in the liver. In 2010, 0.7–1 μmol/g was considered adequate, but this range is considered high (updated in 2015) until more biologically meaningful data are generated.* 
