Abstract: Vitamin B6 in sufficient amounts is needed to serve as the cofactor in many metabolic pathways. These pathways are involved in protein metabolism, brain and nervous system function, and glucose homeostasis. During pregnancy, vitamin B6 is needed for proper fetal development, the avoidance of pregnancy complications, and can be used in the treatment of nausea. Luckily, it is present in many types of food, however, consuming amounts above the RDA is smart. Supplementing with either the pyridoxine or PLP forms can be beneficial. 

What is Vitamin B6? Why Do I Need It?  

Vitamin B6 is a water-soluble vitamin that plays a vital role in many metabolic processes as a cofactor, activating and encouraging many enzymatic reactions. Pyridoxal 5' phosphate (PLP) and pyridoxamine 5' phosphate (PMP) are the active forms of B6 and are involved in amino acid metabolism and carbohydrate and lipid metabolism. Vitamin B6 activates several pathways in amino acid (protein) metabolism that lead to neurotransmitters (such as serotonin, norepinephrine, and gamma-aminobutyric acid) formation, the synthesis of hemoglobin and red blood cells, and myelin sheath formation, the protective layer around nerves. In this way, vitamin B6 aids in the central nervous system's normal development and influences cognitive function. Vitamin B6 also lowers the level of homocysteine, which is considered a risk factor for cardiovascular disease when elevated. 

Maintaining adequate vitamin B6 status might contribute to prevention and treatment of insulin resistance in conditions associated with inflammation and oxidative stress. A current literature review shows evidence that the dysregulation of the tryptophan to kynurenine and kynurenine to nicotinamide adenine dinucleotide (NAD) metabolic pathways are causes of insulin resistance. These pathways are regulated by enzymes influenced by pro-inflammatory factors and/or stress hormones. Pyridoxal-5-phosphate (P5P) is a cofactor in these essential pathways. Deficiency of P5P causes the pathway to produce a type of acid in excessive amounts instead of NAD. This acid impairs the production and activity of insulin, thus the connection to insulin resistance. 

Lastly, this essential nutrient helps support mood and enhances sleep. It promotes healthy digestion and a calm stomach. And contributes to immune function through the production of lymphocytes and interleukin-2. 

Why Is Vitamin B6 Important During Pregnancy? 

There are three main ways vitamin B6 levels impact pregnancy - pregnancy complications, proper fetal growth, and morning sickness/nausea. 

Pregnancy Complications: Research shows that adequate vitamin B6 levels before conception and early in pregnancy may help to prevent pregnancy loss. The risk of developing preeclampsia, a pregnancy complication characterized by high blood pressure, is associated with suboptimal levels of vitamin B6. And lastly, research studies showed several pregnant women with anemia who were nonresponsive to iron supplementation were vitamin b6 deficient. In these cases, the anemia improved with the administration of vitamin b6. 

Proper Fetal Growth: Vitamin B6 is involved in your baby's brain and nervous system development through neurotransmitter synthesis. Case-control studies have shown a possible decrease in the risk of cleft lip and/or palate in babies of mothers who supplemented with folate and consumed high dietary amounts of vitamin B6 before conception. A lack of proper balance among the essential B vitamins (B6, B12, and Folate) can hinder fetal development. Vitamin B6 is also thought to play a role in preventing preterm birth. 

Morning Sickness/Nausea: Vitamin B6 supplementation may help reduce nausea in pregnancy. 

Does Vitamin B6 Reduce Nausea? 

Vitamin B6 (pyridoxine) is considered a first-line treatment for nausea and vomiting in pregnancy by the American College of Obstetrics and Gynecology. 

The American Congress of Obstetrics and Gynecology (ACOG) recommends 10-25 mg of vitamin B6 three or four times a day to treat nausea and vomiting in pregnancy. If the condition does not improve, ACOG recommends adding doxylamine (an antihistamine). Randomized trials have shown that a combination of vitamin B6 and doxylamine is associated with a 70% reduction in nausea and vomiting and lower hospitalization rates for this problem during pregnancy. 

However, prospective studies on vitamin B6 supplementation to treat morning sickness have shown mixed results. In two randomized, placebo-controlled trials, 30-75 mg of oral pyridoxine per day significantly decreased nausea in pregnant women experiencing nausea. Conversely, the authors of a recent review of studies on interventions for nausea and vomiting in pregnancy could not draw firm conclusions on the value of vitamin B6 to control the symptoms of morning sickness. Overall, vitamin B6 is rated as possibly effective in treating pregnancy-induced nausea and vomiting. 

Vitamin B6 Supplementation - What Form Is Best?

The most common vitamin B6 form in supplements is pyridoxine (in the form of pyridoxine hydrochloride [HCl]), although some supplements contain PLP, the most bioavailable form. Pyridoxine has been associated with neurotoxicity and neuropathy only at high supplemental doses above 100 mg/d. Pyridoxal-5'-phosphate has not been associated with neuropathy at high doses.

The absorption of vitamin B6 from supplements does not differ substantially among the various forms of supplements. Bioavailability of vitamin B6 is estimated to be >75% from food in a mixed Western diet and >90% from supplements.

How Much Vitamin B6 Do I Need? 

The RDA for pregnancy is 1.9 mg. 

However, 11% of vitamin B6 supplement users and 24% of people in the United States who do not take supplements containing vitamin B6 have low plasma PLP concentrations. The NHANES analysis from 2003-2004 showed that plasma PLP concentrations were low even in some groups that took 2.0 to 2.9 mg/day, which is higher than the current RDA. The study also showed that regardless of supplementation use at this dose, plasma PLP levels were much lower in women than in men, non-Hispanic blacks than non-Hispanic whites, current smokers than never smokers, and underweight people versus those of normal weight. H4: The study suggested that with this data in mind, the current RDAs might not guarantee adequate vitamin B6 status in many population groups.

Furthermore, a mild excess of supplemental vitamin B6 is unlikely to cause any adverse effects for you or your baby, and supplementation above the daily recommended dose has been used for decades to treat nausea in pregnant women. Research shows that doses of 50 mg or more per day during the first trimester do not cause detrimental effects. However, it is important to note that the Institute of Medicine did establish an upper limit for vitamin B6 of 100 mg/day. 

Other groups at risk for deficiency and low PLP plasma concentrations are those with alcohol dependence, obesity, preeclampsia/eclampsia, and malabsorption syndromes, such as celiac disease, Crohn's disease, and ulcerative colitis. Other risk factors for low plasma PLP amongst women of reproductive age include those that are having multiples and those that have used oral contraceptives in the past. Lastly, the anti-tuberculosis drug isoniazid interferes with vitamin B6. If you are at an increased risk of deficiency, consuming more than the RDA for vitamin B6 is advisable. 

Am I Getting It From Food? What Food Sources Contain Vitamin B6? 

Vitamin B6 is present in moderate quantities in a wide variety of foods. Good food sources include baked potatoes, salmon, chicken, cooked spinach, prune juice, chickpeas, brown rice, bananas, peas, beans, avocados, and pork loin, among many others. Fruits, other than citrus, are a rich source of the vitamin, as well. 

• • • 1 cup of chickpeas is 1.1 mg per serving 
    • 1 cup of boiled potatoes 0.4 mg 
    • 1 medium banana 0.4 mg

How Can I Tell If I Am Getting Enough Vitamin B6? 

Vitamin B6 concentrations can be assessed by measuring concentrations of PLP or total vitamin B6 in plasma, erythrocytes, or urine. Plasma PLP is the most common measure of vitamin B6 status. However, vitamin B6 status is best assessed by using a combination of biomarkers because of the influence of potential confounders, such as inflammation, low serum albumin, alcohol consumption, and renal function. 

PLP concentrations of more than 30 nmol/L have been traditional indicators of adequate vitamin B6 status in adults. However, the Food and Nutrition Board (FNB) at the Institute of Medicine used a plasma PLP level of 20 nmol/L as the indicator of adequacy to calculate the RDAs for adults. This is another reason why the calculated RDA may be too low for Vitamin B6. 

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Prenatal Analysis

All of the vitamin B6 amounts included above are either at or above the pregnancy RDA. Based on our research, we know that not only is it safe to go significantly above the RDA for B6, it is advisable in many cases. Furthermore, all amounts listed above are significantly below the Tolerable Upper Limit of 100 mg/day. The bioavailable P5P form is utilized in multiple vitamin formulations, but we also see pyridoxine HCl used a couple of times. Several studies have shown non-significant absorption differences between the two forms. 

Resources:

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