Vitamin A Spotlight

Tuesday, 17 November 2020

Vitamin A, a fat-soluble vitamin is involved in regulating the growth and specialization of virtually all cells in the human body, playing important roles in embryonic development, organ formation during fetal development, ovarian health, normal immune functions, and eye development and vision

Vitamin A is a generic term that refers to compounds found as preformed vitamin A (retinol) in animal products that include dairy, liver, and fish oils (hence the use of cod liver oil) and as provitamin A carotenoids in fruit and vegetables that include: Apricots, carrots, mangoes, pumpkin, squash (yellow and winter), sweet potato and green vegetables, such spinach and broccoli.

The three active forms of vitamin A in the body are retinol, retinal, and retinoic acid - referred to as retinoids.

Beta-carotene (provitamin A) can be converted to biologically active retinoids by the BCO1 gene. Variants on this BCO1 gene reduces someone's ability to convert beta-carotene by more than 50%. Here is my genetic profile, from LifecodeGx. As you can see I am a very poor converter:

And so I do supplement twice a week to keep my levels up. 

Some more detail of the functions of Vitamin A 

Vitamin A and the immune system: 

Vitamin A was initially coined “the anti-infective vitamin” because of its importance in the normal functioning of the immune system. The skin and mucosal cells lining the airways, digestive tract, and urinary tract function as a barrier and form the body's first line of defense against infection. Retinoic acid (RA) is produced by immune cells - including macrophages and dendritic cells, found in these mucosal interfaces. RA is also required for the differentiation of naïve T-lymphocytes into regulatory T- lymphocytes (Tregs), nicknamed the policeman/woman of the immune system. As well RA induces the production of proinflammatory signals by other immune cells in response to infection -  so helps “fight” bacteria and viruses.

Barrier integrity:

Vitamin A plays a vital role in maintaining gap function between cells, maintenance of myelin sheath membrane and maintains lysosome stability and mucosal barrier to infection.

Prenatal and postnatal development

Both vitamin A excess and deficiency are known to cause birth defects. Retinoid signaling begins soon after the early phase of embryonic development known as gastrulation. During fetal development, RA is critical for the development of organs, including the heart, eyes, ears, lungs, as well as other limbs and visceral organs. 

Red blood cell production (erythropoiesis)

Red blood cells (erythrocytes), like all blood cells, are made from stem cells in the bone marrow. Vitamin A appears to facilitate the mobilization of iron from storage sites to the developing red blood cell for incorporation into hemoglobin, the oxygen carrier in red blood cells. The combination of supplemental vitamin A and iron seems to reduce anemia more effectively than either supplemental iron or vitamin A -  which is super interesting! 

Eye & Brain development

Vitamin A supports hippocampal retinoid receptor pathways that are critically involved in vision” sensory perception, language processing and attention

Ovarian health

Deanne Minich, a highly esteemed  lifestyle medicine expert wrote “There is some indication that the foods you eat may influence the decline of ovaries. A study with 1,146 pre-menopausal women followed up for an average of 12.5 years using a self-reported food frequency questionnaire found that the onset of natural menopause was correlated with dietary intake of the carotenoid pigment, even after adjusting for other factors (e.g, BMI, physical activity level, education, smoking, energy, and alcohol intake). Statistically, both β-cryptoxanthin and fruit intake were associated with a significant delay in the onset of natural menopause. The researchers concluded that “a diet containing ∼400 micrograms of β-cryptoxanthin (a natural carotenoid pigment in mandarins, oranges, and peaches) has significant potential to delay ovarian senescence by 1.3 years.”

So, if you were to eat more of these orange fruits, how much would you need to hit the 400 microgram target? Here are the amounts of beta-cryptoxanthin in certain foods:

  • A persimmon — about 2,400 micrograms

  • A large tangerine — about 488 micrograms

  • Tangerine juice is even higher than a tangerine at 529 micrograms in 1 cup

  • One orange — about 170 micrograms

Reference: Karma Pearce & Kelton Tremellen (2016) Influence of nutrition on the decline of ovarian reserve and subsequent onset of natural menopause, Human Fertility, 19:3, 173-179, DOI: 10.1080/14647273.2016.1205759

Well established signs and symptoms of vitamin A deficiency include

  • Acne (its role in barrier integrity and inflammation)
  • Allergies (its role in immune cell differentiation)
  • A decrease in the  function of neutrophils and natural killer cells which form an important part of our innate immune system
  • Dry hair, rough and dry skin 
  • Inflammation of the eye, sinus problems and dry eye

Signs and Symptoms of Toxicity​:

Most commonly, nausea, vomiting, and headache. In extremes, anorexia, blurred vision, scaling skin, hair loss (alopecia), organ damage, Osteopenia and osteoporosis can be worsened by vitamin A at non-toxic levels when vitamin D and calcium are deficient. It is prudent to keep vitamin A below 10,000 IU per day during the first eight weeks of pregnancy due to a possible risk of birth defects unless blood measurements, signs, and symptoms justify higher intakes to prevent deficiency.

An important note: 

Vitamins A, D, E, and K are all fat-soluble. Dietary fat enhances their absorption, so, disorders that cause fat malabsorption, such crohn’s disease, coeliac disease, cystic fibrosis, and a rather large collection of disorders of the liver, pancreas, gallbladder, bile ducts, and small intestine can cause deficiencies of all four vitamins.

Fat malabsorption can also cause deficiencies of saponifiable minerals. Saponification is the process of a mineral binding to a fatty acid. The most relevant minerals include sodium, potassium, calcium, and magnesium, and to some extent iron, zinc, copper, and manganese may also be affected.

Low levels of all four fat-soluble vitamins, rather than low levels of only one is the best way to assess this, and your practitioner can assess for this on a blood test.  

Zinc is necessary for virtually every step in vitamin A metabolism, including its transport in the blood. Zinc deficiency should ​always​ be considered as an explanation for an apparent case of vitamin A deficiency.

Dosing:

The Recommended Dietary Allowance (RDA) for men and women is 900 and 700 μg retinol activity equivalents (RAE)/day, respectively. The Tolerable Upper Intake Level (UL) for adults is set at 3,000 μg/day of preformed vitamin A. My favourite supplement is a product called Beta Immune + that contains preformed Vitamin A and D and zinc at these levels:


 

Finally how do I assess the B-carotene equivalent?

The international standard of measure for vitamin A is retinol activity equivalents (RAE), which represent vitamin A activity as retinol. It has been determined that 2 micrograms (μg) of β-carotene in oil provided as a supplement could be converted by the body to 1 μg of retinol giving it an RAE ratio of 2:1. However, 12 μg of β-carotene from food is required to provide the body with 1 μg of retinol, giving dietary β-carotene an RAE ratio of 12:1. Other provitamin A carotenoids in food are less easily absorbed than β-carotene, resulting in RAE ratios of 24:1. RAE ratios are shown in this  Table

In health, Tanya x