Why is vitamin D so important for children and adults?
At LittleDot, our mission is to build a long-term relationship of trust and health with every parent and child. One essential pillar of lifelong wellbeing is vitamin D—a vital component in bone development, immune function, and disease prevention.
What is vitamin D and how is it produced?
Vitamin D refers to a group of fat-soluble compounds, with vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) being the most significant.
– Vitamin D2 is produced by plants, fungi, and invertebrates.
– Vitamin D3 is synthesized by vertebrates, including humans.
Vitamin D obtained from sunlight (through UV-B exposure) or food is biologically inactive until processed by the body. The skin synthesizes vitamin D when exposed to UV-B rays with wavelengths between 270 and 300 nm, typically when the solar index is 3 or above. Synthesis occurs in the deeper layers of the skin.
Who is at risk of vitamin D deficiency?
Individuals with increased melanin (darker skin tones) have natural protection against UV radiation. However, this same protection reduces the efficiency of vitamin D synthesis. As a result, dark-skinned individuals living in northern latitudes are at higher risk of vitamin D deficiency. Conversely, fair-skinned people in high UV areas, such as Australia, face increased risks of skin cancer and melanoma.
What affects the synthesis of vitamin D?
Vitamin D synthesis from sunlight is influenced by:
– Geographic latitude
– Season and time of day
– Cloud cover and air pollution
– Clothing and time spent outdoors
– Use of sunscreens and UV-blocking products
UV-B exposure is generally adequate year-round in tropical regions, seasonally sufficient in temperate climates, and chronically low in Arctic zones.
Dietary sources of vitamin D
While sunlight remains the primary natural source, vitamin D is also present in food—although typically in small amounts. Some key sources include:
– Cod liver oil: 15 ml contains ~1,360 IU
– Oily fish (e.g., sardines and tuna): 250–200 IU per serving
– Egg yolks: ~20 IU
– Liver and UV-exposed mushrooms
Fish contain vitamin D because they feed on algae that synthesize the vitamin through sunlight exposure. To address widespread deficiency, many countries fortify basic foods such as milk, margarine, oils, pasta, and bread.
How does vitamin D work in the body?
Once synthesized or ingested, vitamin D must undergo two hydroxylation steps—in the liver and kidneys—before it becomes biologically active. The final product, calcitriol (1,25-dihydroxycholecalciferol), binds to carrier proteins in the bloodstream and travels to target tissues.
In this active form, vitamin D:
– Stimulates protein synthesis
– Promotes calcium absorption in the intestines
– Helps regulate calcium and phosphorus levels in blood and bone
– Works with parathyroid hormone and calcitonin to maintain skeletal health
Health consequences of vitamin D deficiency
In children, vitamin D deficiency leads to rickets—a disease that results in:
– Softened and deformed bones
– Impaired growth
– Developmental delays
Systematic prophylaxis using vitamin D3 supplementation during infancy has dramatically reduced the incidence of rickets in developed countries.
Vitamin D and systemic health
Vitamin D is not just a skeletal nutrient. It influences the expression of hundreds of genes and affects multiple organ systems. It plays a critical role in:
– Brain, heart, skin, breast, and prostate health
– Cell proliferation and differentiation
– Immune system regulation (present in monocytes, T cells, and B lymphocytes)
Ongoing studies explore its potential in managing autoimmune conditions (e.g., type 1 diabetes, lupus, rheumatoid arthritis), neurological disorders (e.g., multiple sclerosis), and even various cancers (e.g., prostate, colorectal, breast, and leukemia).
Recommended daily intake of vitamin D3
– Infants (1–12 months): 400–1,000 IU daily
– Children and adults up to age 70: 400 IU (with some sources recommending up to 2,000 IU)
– Adults over 70: 600 IU
After the first year of life, supplementation is often advised during winter months. For those with light skin, 20 minutes of sun exposure daily may suffice. Individuals with darker skin may require 60 to 120 minutes daily to achieve similar synthesis.
The body has a natural limit to how much vitamin D it can produce from sunlight, and excess amounts are broken down efficiently, preventing overdose from sun exposure.
Is It safe to take vitamin D supplements?
Yes. While there is a wide range between the recommended and upper daily limits (up to 10,000 IU in some guidelines), vitamin D toxicity is rare. When used as directed, multivitamins and D3 supplements are safe and effective in addressing deficiency, especially in climates or lifestyles that limit sun exposure.
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