Nutrient Spotlight: Vitamin A

The advice to eat carrots for good eyesight is one many of us heard throughout childhood. Though simple, this advice is actually grounded in science. Carrots contain the fat soluble nutrient vitamin A, which has long been implicated in maintenance of ocular (eye) health. However, it does so much more! Before we dive into the biology of it all, here's some important lore for you:

Vitamin A was actually the first vitamin identified by researchers. In the 1800s, researchers found that corneal (referring to the cornea of the eye) ulcers followed nutrition deprivation in dogs and a similar finding was also noted in undernourished abandoned children in Paris. The nutrient was finally named in the early 1900s as Vitamin A. Although the previously mentioned findings point to it's role in eye health, over a century of subsequent research has shown that its influence on the body extends well beyond this, touching everything from immune function to skin integrity.

Carrots: Source of Vitamin A

Vitamin A is a fat soluble vitamin that exists in two forms: preformed vitamin A (found in animal sources) and provitamin A carotenoids (found in plant sources). Provitamin A carotenoids (e.g. beta carotene) are converted into vitamin A in the intestines. Vitamin A is dependent on the presence of fat in order to be absorbed. It is involved in regulating immune function, reproduction, cellular communication, growth and development, eye health and also skin health.

Role of Vitamin A in Immunity

Vitamin A is essential to the healthy functioning of the thymus, where immune cells mature, and a deficiency in this nutrient can impair the body's ability to mount effective immune responses through both T cells and antibodies. Vitamin A also shapes innate immunity, which is the body's first line of defense. It helps to regulate macrophages, neutrophils, and dendritic cells, and supports specialized cells that protect the intestinal lining from bacterial invasion. Its influence extends to T cells as well, helping guide these cells to where they are needed most. T cells keep the immune system in balance and prevent it from attacking the body's own tissues. The nutrient also supports antibody-producing B cells, contributing to the production of immunoglobulins that help the body fend off infection.

Role of Vitamin A in Reproduction

Vitamin A is also essential to reproduction in both males and females. In males, it is required for sperm production, and deficiency halts this process. However, production can resume once vitamin A is restored. In females, the timing and severity of vitamin A deficiency can influence fertilization, cause embryonic loss or placental complications later in pregnancy. At the cellular level, vitamin A also helps guide the process by which developing sperm and egg cells prepare for fertilization through meiosis. Overall, the evidence points to vitamin A as fundamental to fertility and to the healthy development of reproductive cells from their earliest stages.

Beef Liver: Source of Vitamin A

Role of Vitamin A in Growth and Development

Vitamin A plays a central role in guiding growth and development throughout the body. Once converted into its active form, it binds to receptors that regulate gene expression, effectively directing when certain genes are switched on or off. This process is essential during pregnancy, shaping the formation of the heart, limbs, eyes, and nervous system, and both deficiency and excess during this period can lead to developmental abnormalities. Vitamin A also governs how cells differentiate into their specialized roles, while supporting healthy bone growth and eye development.

Role of Vitamin A in Eye Health

Within the retina, vitamin A is converted into retinal, a compound that combines with a protein called opsin to form rhodopsin, the light-sensitive pigment found in the eye's rod cells. Rhodopsin is critical for vision in low-light conditions, which is why vitamin A deficiency often first presents as night blindness. Beyond this core function, vitamin A also supports the health of the cornea and conjunctiva, and prolonged deficiency can lead to a condition known as xerophthalmia, characterized by severe dryness and, in advanced cases, irreversible damage to the eyes. Given its central role in both everyday vision and the prevention of serious ocular disease, vitamin A remains one of the most well-established nutrients for eye health.

Role of Vitamin A in Skin Health

Vitamin A plays a significant role in maintaining healthy skin by regulating the growth and turnover of skin cells. It supports keratinocyte differentiation, helping cells in the outer layer of skin mature and shed normally rather than building up and roughening the skin's texture. This is part of why deficiency is often associated with dry, thickened, or flaky skin. Retinoids, compounds derived from vitamin A, are also widely used in dermatology to treat acne and reduce visible signs of aging, as they can stimulate collagen production.

Recommended Dietary Allowance for Vitamin A

The recommended dietary allowance for Vitamin A are denoted as retinol activity equivalents. This account for the varying biological activities of retinol and provitamin A carotenoids (all converted to retinol in the body):

900ug RAE- Men

700ug RAE- Women

Sweet Potato: Source of vitamin A

Sources of Vitamin A

Sources of Vitamin A ranked by microgram of Retinol Activity Equivalents (RAE) content:

Beef Liver 6582

Sweet Potato 1403

Spinach 573

Carrot 459

Milk 149

Sweet Red Pepper 117

Mango 112

Egg 75

Black Eyed Peas 66

Broccoli 60

Salmon 59

Tuna 20

Chicken Breast 5

Pistachios 4