This study demonstrated statistically significant t test variations for the TG in comparison to the population data in all 18 parameters studied except cholesterol. Although the t test result for cholesterol was not significant, 40% were outside the RI, with relatively equal results above and below the RI. T test results for the subgroups also showed significant variations.
AN is a condition characterized by protein energy undernutrition, and sufferers may show deficiencies in minerals and electrolytes largely derived from protein sources such as zinc, potassium, phosphate and calcium, in addition to vitamin D deficiency .
Particularly striking was the consistently low level of manganese, considered a factor in mental health as early as the 1920s . Manganese is important for enzymes involved in carbohydrate metabolism, and for connective tissue/cell membrane integrity. Manganese deficiency may result in osteoporosis, impaired insulin production, alteration in lipoprotein metabolism, an impaired oxidant defence system, fatigue, and abnormalities in growth factor metabolism . It can also be associated with epilepsy, dizziness and schizophrenia [36,37,38,39]. However, neurological toxicity has been reported at high doses, including Parkinson’s disease-like side effects  therefore any supplementation requires careful monitoring. A World Health Organization (WHO) report  suggested that only very rarely has research found significant deficiency in the level of manganese in humans - which suggests the low manganese in our population may be very significant.
Zinc levels were significantly reduced, which has previously been reported in patients with AN and those suffering from schizophrenia . Birmingham et al. found that AN patients treated with zinc supplements showed a rate of BMI gain twice that of a placebo group . Zinc is critical for the functioning of enzyme reactions including neurotransmitter synthesis . Low levels of zinc can result in altered taste perceptions, loss of smell and a decrease in appetite . A 2015 nursing home study demonstrated improved cognitive performance and mood in patients with higher levels of serum zinc . It has been suggested that all patients with AN should be given zinc supplements .
Phosphate is important for cellular energy (ATP formation) and its deficiency is of particular concern during re-feeding. Although serum phosphate may be initially normal, body stores are likely to be low and increased metabolism with re-feeding can cause precipitous falls, with consequent muscle weakness and risk of cardiac failure . Excessive intake of phosphate can lead to bone impairment and ageing . The higher than expected phosphate levels in this study may relate to variability in severity and/or phosphate supplementation.
Magnesium is a co-factor in over 300 enzymatic reactions known to be important in the normal functioning of muscles, nerves, heart, bones, and the immune system, in regulating potassium fluxes and in the metabolism of calcium [46, 47]. Magnesium deficiency has also been linked to stress, anxiety , and excitability or depression . Significant falls during re-feeding in EDs are well documented ). Therefore, although this study did not show any patients outside the RI the authors strongly recommend magnesium be routinely measured throughout diagnosis and treatment. Serum magnesium reflects less than 1% of body stores, however low serum levels are a simple and accurate means for assessment of acute changes in magnesium status .
Ferritin stores and transfers iron in a non-toxic form in the body. Iron is necessary for the production of haemoglobin and red blood cells. It is also considered critical for proper brain function and, as levels drop, depression and fatigue may develop . Study results indicated that one third of TG patients scored below the population RI, while only a small percentage were high. As ferritin is an acute phase reactant however levels may not necessarily reflect iron stores [50, 51].
Although cholesterol levels failed to reach significance levels in the t-test analysis, it was noted that the TG showed 19% of patients to have cholesterol levels below the RI, and 21% above the RI. Theories have been proposed for the paradoxical elevation of cholesterol in those with severe EDs including being related to low levels of thyroid hormones resulting in reduced metabolism of existing cholesterol [52, 53]. Low levels of cholesterol have been associated with depression, anxiety and suicidal tendencies [54,55,56,57,58]. Impaired cholesterol synthesis may explain the low cholesterol in some individuals . In vivo cholesterol synthesis is a complex process requiring multiple nutrients including manganese [39, 59]]. This is of particular significance in the context of the low manganese levels in the study population.
Reduced metabolism may explain the significantly elevated results for vitamin B12 and folate and the absence of low levels relative to the RIs. Both folate and vitamin B12 were found to be low prior to the introduction of voluntary folate additives in 1998, made compulsory by the Australian Government in 2009 . The National Centre for Environmental Health in the US reported a small increase in serum Vitamin B12 following fortification . It is accepted that high levels of folate and vitamin B12 are not normally a problem as long as they occur together, while low levels of folate are today rare and often not clinically monitored . It has been shown that cells require vitamin B12 to utilize folic acid. Thus, if B12 is too low, folic acid may accumulate . Vitamin B12 is essential for the formation of red blood cells and the health of nerve tissue .
Vitamin D levels were significantly reduced with implications for bone health, mental health and a potential susceptibility to the development of breast, lung and bowel cancers, multiple sclerosis, diabetes, auto-immune disorders, allergies and depression [64, 65]. Modan-Moses et al. reported a high prevalence of vitamin D deficiency in adolescents with EDs and suggested supplementation as required .
Calcium is important for nerve conduction, muscle contraction and metabolism of bones and teeth.(39). The study showed slightly elevated serum levels, but as ionised (free) calcium is considered a more reliable measure (49) this result is of uncertain significance.
Potassium and sodium were found to be significantly outside the RIs in the TG and AN subgroup while no significant deviation from the RI was found in other subgroups. Sodium and potassium are essential for cellular homeostasis, including proper functioning of nerves and muscles, including the heart. Hypokalaemia has been associated with cardiac arrhythmias which are believed to be a cause of mortality in EDs [67, 68].
Albumin is important in maintaining intravascular volume and transfer and metabolism of a large variety of molecules. The study found significantly higher levels in the TG, AN and AN/BN subgroups. Hyperalbuminaemia is commonly related to dehydration , although this explanation would seem somewhat incongruous in the ED population. Unfortunately, hydration levels of patients at the time of testing are unknown. Most patients with anorexia nervosa have normal serum albumin levels (49). The Minnesota starvation experiment demonstrated that even with a 23% reduction in body weight and muscle mass, serum albumin decreased only moderately. It has been noted that malnutrition in the absence of inflammation does not usually result in significant falls in serum albumin, probably because of compensatory reductions in albumin fractional catabolic rate and resting energy expenditure .
Urate, or uric acid, is the end product of purine metabolism in humans. It represents over 50% of the blood’s anti-oxidant capacity, but chronically high levels may be associated with gout and metabolic syndrome. It is not known whether elevated levels represent a risk factor or a protective factor. Production of lactate and ketone bodies can inhibit uric acid excretion, which may contribute to elevated levels in eating disorders .
Although haematological parameters in this study showed small variations from normal, they were statistically significant. Considering the risk of anaemia, neutropenia and thrombocytopenia in EDs, the value of monitoring the full blood count (FBC) is beyond question . As with other results such as potassium, albumin, magnesium and phosphate, the low number of severe abnormalities may reflect a less severe degree of illness in patients presenting in a general practice as opposed to a hospital setting,
Limitations of study
As this study is retrospective not all data were available for analysis. For some patients the initial consultation represented the first medical contact, whilst others had been within the medical system for some time. As such, previously initiated treatment regimes including dietary manipulations, additional supplements, psychiatric and medical interventions, all of which may be relevant, were not available. Full clinical information, including but not limited to vomiting, laxative intake, dietary intake, amount of exercise and intake of drugs and alcohol, were not included. Ethics approval was granted on the specific condition that patients who chose to participate would not be identifiable by the GP, and collection of this material could have threatened this condition.
Blood samples were not specifically collected in a fasting state (as this may jeopardise patient safety in an outpatient population) and there is no information available as to degrees of supplementation or oral intake prior to collection of any samples.
Although this medical practice has a disproportionately large number of patients diagnosed with EDs, sample sizes, particularly of some subgroups, were small. For this reason, statistical analysis was limited.