Glycine and pregnancy: an essential amino acid?

The body has additional glycine requirements during pregnancy, such that, according to studies, the demand for glycine during pregnancy could exceed the body's capacity to synthesise it, making glycine "conditionally essential"[2]. Studies show that glycine synthesis, particularly towards the end of pregnancy, is clearly insufficient to meet requirements, making glycine indispensable during this period [3]. 

The previous study also shows that glycine synthesis is inadequate to meet the foetus's glycine requirements. Placental glycine production is not a sufficient source of glycine for the foetus [4].

The physiological and hormonal changes that occur during pregnancy increase the risk of arthritis [6]. Arthritis during pregnancy has been associated, among other things, with an increased risk of pre-eclampsia and caesarean section [7]. Glycine consumption may increase collagen synthesis, which could help with cartilage regeneration and strengthen joints, thereby reducing the risk of arthritis [8]. 

The foetus requires a significant supply of glycine, and a suboptimal intake may have consequences for its development [10]. For example, adding glycine to a low-protein diet can reverse the increase in blood pressure caused by such a diet [11]. 

It appears that supplemental glycine improves vascular function in both the mother and her baby. It has been suggested that a mother fed a glycine-enriched diet is better able to adapt her vascular system to the demands of pregnancy, thereby protecting the foetus from potential cardiovascular problems caused by restriction of uterine blood flow [10].

This effect of glycine may be due to the fact that it provides the methyl groups necessary for the synthesis of methyl tetrahydrofolate (the active form of folate) and determines the availability of methylated folates. This reconstitution of the methylated folate pool may explain the reversal of the hypertensive effect observed when the diet is supplemented with glycine [12]. In addition, as glycine is required for a number of critical metabolic pathways — such as the synthesis of structural proteins including collagen and elastin — disruption of these pathways leads to impaired elastin formation (a protein with elastic properties) in the aorta [13].

Women with pre-eclampsia excrete less glycine, which suggests an increased demand for glycine and/or low maternal glycine reserves [14]. Glycine may have a protective effect against oxidative stress [13], a marker of pre-eclampsia, and studies have shown that it may help reduce blood pressure and blood sugar levels [15].

Furthermore, low glycine levels have been observed in premature infants [16].

Glycine plays a central role in the synthesis of glutathione synthase. Glutathione synthase, which is formed from cysteine, glutamate, and glycine, is the most abundant intracellular non-protein molecule and plays essential roles in protection against oxidative stress and in the regulation of protein synthesis and cellular DNA — particularly important during pregnancy. Glycine therefore plays a role in the synthesis of foetal DNA. Choline, which is involved among other things in methyl group metabolism (reduction of homocysteine, implicated in neural tube defects), depends in part on glycine for its metabolism [16]. 

Therefore, an optimal intake of choline and glycine is necessary for the healthy development of your baby.

Glutathione (formed from glycine) is involved in the detoxification of xenobiotic compounds (such as medications and pesticides) and endogenous compounds (toxins formed by the body). Glutathione facilitates the transport of toxins across the plasma membrane. Low levels of glutathione and/or activity are associated with chronic exposure to chemical toxins, cadmium exposure, and neurodegenerative disorders [17].

The elimination of toxins is particularly important for maternal and neonatal health. For example, exposure to pesticides has been linked to an increased risk of gestational diabetes [18] and can impact embryonic development [19].