Vitamin D is often referred to as the “sunshine” vitamin, as it is produced by the human body in response to sunlight exposure. Humans have a unique way of producing and using vitamin D that is very different from other nutrients. The human body actually synthesizes vitamin D in response to UV rays from the sun, specifically UVB (1). The processes that our cells undergo to synthesize vitamin D are complex and require several modifications to the compound before it can be used by the body. However, once vitamin D reaches its most bioavailable form, it is used in many different parts of the body (2).

What is its role in the body?

Vitamin D is an essential vitamin for the body and plays a critical role in several key bodily functions, especially during child growth and development.

Healthy Bones

One of the first functions that the vitamin was credited with was its ability to help cure rickets, a disease that causes weak and soft bones. Thusly, sufficient vitamin D is a major component in maintaining bone health (3). Vitamin D is a crucial facilitator for the absorption of calcium and phosphorous into the bones. Both of these compounds are necessary to maintain bone strength and density, and without them, bones become soft, weak, and cause pain. However, without the presence of vitamin D, neither of these compounds would be able to reach their final destination (4). Rickets most often occur in children from a lack of vitamin D or calcium in their diet. While rickets are very rare in developed countries, children with darker skin are at a higher risk because they must be exposed to more sunlight than fairer children (5).

Immune System

The immunological benefits of vitamin D have only become well-researched in recent years. The first indication that vitamin D could be used to improve immune function was its role in the treatment of tuberculosis almost a century ago. The use of cod-liver oil – a substance high in vitamin D – and exposure to sunshine in sanatoriums were treatments that involved the use of vitamin D, though this was not known at the time (6). The way vitamin D contributes to immune function is in regulating cellular growth and proliferation. It can suppress proliferation of T and B cells which are key units of the innate immune system. Suppression is often seen as a negative effect, but in this case, vitamin D actually reduces the number of inflammatory immune cells in the body, and ensures that these immune cells do not attack self (7). Proper development of the immune system is particularly important in infancy and childhood, and studies show that vitamin D can be a key player in this aspect of development.

How does your child get sufficient vitamin D?

The easiest answer to a vitamin D deficiency is getting more sunlight. Less than half an hour of sun exposure is long enough to trigger synthesis of vitamin D in the skin. However, strict adherence to sun protection should not be ignored, especially for delicate baby skin (8). Fortified milks – plant milks and cow’s milk, alike — can be a good source of vitamin D, as they are typically supplemented with vital nutrients (1). Studies also indicate that vitamin D levels in pregnant women can impact the development of their unborn child, indicating that proper nutrition during pregnancy is particularly important (9). What’s more, mother’s milk typically does not contain sufficient vitamin D for infants either, so supplementation is needed during the first six to twelve months of life. Formula is usually better equipped to meet vitamin D needs in infants, but it is always important to do research on the nutritional profile of different formulas(10).

When your child becomes older and begins to eat solid foods, there are more dietary sources that can provide vitamin D. Salmon, trout, and fish oil contain high amounts of vitamin D. Mushrooms are high in vitamin D, as well, along with fortified milks and cereals (2). These are all great foods to add to your child’s diet, but picky eaters may have more difficulty warming up to oily fish and mushrooms, so supplementation will likely continue to be necessary.

While dietary supplementation is crucial for upping your child’s intake of vitamin D, never underestimate the numerous benefits of a bike ride or walk in the park on a sunny day. Not only will the sunlight help you and your child synthesize more vitamin D, but you will be instilling the importance of exercise and fresh air in your child, practices that contribute to a healthy and active lifestyle!

Nicole Avena, PhD, is Assistant Professor of Neuroscience at Mount Sinai School of Medicine and Visiting Professor of Health Psychology at Princeton University. She is the author of several books, including What to Feed Your Baby and Toddler, and What to Eat When You’re Pregnant.  The post was adapted from What to Feed Your Baby and Toddler.


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