Table 3. Risk Factors for Low Serum Retinol (<0.7 lmol/L) Among Women and Children OR 95% CI P Children Non-anaemic Anaemic Non-emaciated Emaciated Non-multi-parasitic infection Multi-parasitic infection Age < 12 months Age 12–36 months Age > 36 months Nomads Semi-nomads Sedentary Sex female Sex male Women Non-anaemic Anaemic Non-emaciated (BMI 18 kg/m2) Emaciated (BMI < 18 kg/m2) Non-multi-parasitic infection Multi-parasitic infection Age < 25 years Age 25–35 years Age > 35 years Nomads Semi-nomads Sedentary 1 0.5 1 0.6 1 0.6 1 4.1 15 1 17 27 1 0.8 1 2.2 1 0.3 1 1.8 1 0.3 0.7 1 21 8 0.2–1.7 0.2–2.6 0.2–2.0 0.4–14 2–38 3.4–89.7 4.1–131 0.3–2.5 0.4–8.2 0.1–1.4 0.3–8.6 0.1–2.0 0.1–8.5 2.6–66 1.9–28 0.2 0.5 0.4 0.2 0.01 0.01 <0.01 0.7 0.3 0.1 0.4 0.4 0.8 0.004 0.06 adequate complementary feeding, prevention and/or treatment of malnutrition and the promotion of hygienic practices in environmental sanitation and food preparation and storage. In addition, promotion of local and regional food could be improved. For example, red palm oil, pro- duced in tropical West Africa, is the richest naturally occurring source of b-carotene, and humans can convert this into usable vitamin A as retinol (Rice and Burns 2010; Zagre´ et al. 2003). Limitations of the Study This study was limited by the small sample size of women’s milk. Therefore, it was not possible to develop further statistical analyses, such as the comparison across age groups of breastfed children. Retinol Assessment 119 The study investigated the use of portable devices (Ret 515-2, Ret 435-1 and Hemocue Hb301) in mobile com- munities. These devices are not designed to operate con- tinuously over long periods of time in harsh environmental conditions, which potentially limits the sample size ana- lysed. In this study, two duplicate devices were utilised to avoid this limitation. CONCLUSION At the end of the wet season, nomadic pastoralists have higher blood retinol concentration compared to semi-no- madic and sedentary women and children, who seem to be more vulnerable to deﬁciency. The difference is statistically signiﬁcant and is likely due to higher milk consumption by nomadic pastoralists, as supported by a positive correlation between blood retinol and livestock milk retinol. However, nomadic pastoralist retinol levels may be decreased during the dry season when milk consumption is reduced as a result of lower production and higher milk sales. In the study area, sufﬁcient milk consumption, complemented by dietary fruits and green vegetables, could maintain ade- quate retinol status. It is crucial to implement a programme of food education emphasising the importance of animal based sources of vitamin A such as liver and milk, in addition to locally available products such as Spirulina or plant based products, despite the limited bioavailability of vitamin A precursors from fruits and vegetables. The results support an ecological linkage between human retinol level and livestock milk retinol. The study shows the feasibility of portable retinol measurement in human blood and human and animal milk under remote ﬁeld conditions, but it requires further validation. ACKNOWLEDGMENT This article is dedicated to the memory of Martin Frigg, former head of the Sight and Life Foundation, who pioneered the control of vitamin A deﬁciency. This study has been supported by the Sight and Life Foundation and NCCR North–South, funded by the Swiss Agency for Development and Cooperation and the Swiss National Science Foundation. We would like to thank our partner institutions in Chad, the Centre de Support en Sante´ Internationale and the Laboratoire de Recherches Ve´te´ri- naire et Zootechniques, N’Djame´na, Chad.