Vitamin D Absorption

Vitamin D plays an important role in maintaining calcium and phosphorus levels in the body. Vitamin D, a fat-soluble vitamin, mainly promotes absorption of calcium from digested food into the blood stream and keeps your bones strong.

Two major forms of this vitamin are ergocalciferol or Vitamin D2 and cholecalciferol or Vitamin D3. D2 comes from plants whereas D3 comes from exposure to morning sunlight and consumption of certain foods.

Kidney and liver play an important role in the absorption of this vitamin by converting the biologically inert vitamin D into its active forms, calcitriol and calcidiol respectively.

• It regulates the supply of calcium to bones through blood and vice versa.
• It is responsible for bone growth and bone remodeling by osteoblasts and osteoclasts.
• It prevents rickets (softening of the bones) in children.
• It helps prevent obesity and diabetes.

• It prevents osteomalacia (a bone-thinning disorder) in adults. Weak and fragile bones result in frequent fractures. These adults usually experience musculoskeletal pain.
• It helps fight depression, prostate cancer, breast cancer, osteoporosis, high blood pressure, some cardiovascular diseases, phagocytic activity, etc.

• It boosts anti-tumor activity.
• It controls the release of parathyroid hormone from the parathyroid gland.
• It strengthens the immune system.

A dose of 200 - 400 international units (IU) of vitamin D is sufficient to prevent rickets in children but it is not at all sufficient to maintain your overall health.

According to The Food and Nutrition Board of the Institute of Medicine, 25 mcg (1,000 IU) for infants up to one year of age and 50 mcg (2,000 IU) for children, adults, pregnant and lactating women is the tolerable upper intake level (UL) of vitamin D.

Scientists say, "the minimal daily requirement of vitamin D should be in the range of 2000 - 4,000 IU from all sources, rather than the 200 - 400 IU that is currently suggested."

Vitamin D is found in food but your body can also make it when exposed to ultraviolet rays of the sun. This vitamin exists in various forms but some forms are relatively inactive in your body.

The liver and kidney convert it to its active hormone form. D3 or cholecalciferol is found in animal foods. Most types of milk contain this vitamin. Fatty fish (herrings, kippers, salmon and tuna), liver, egg yolks, cod liver oil and halibut liver oil, etc. are good sources of this vitamin.

Causes of vitamin D deficiency include

• Insufficient dietary intake
• Limited exposure to sunlight
• The kidneys / liver cannot convert the vitamin to its active form

• Gastrointestinal disorders affect the process of absorption of the vitamin in the gut.
• Steroids are taken as anti-inflammatory medication. They lower calcium absorption and impair vitamin D metabolism.

Vitamin D deficiency symptoms are mainly noticed in patients with Alzheimer's disease, post-menopausal women and seniors. The deficiency can lead to abnormal functioning of bodily systems and premature aging. As people grow older, the energy levels decrease. The elderly often prefer to stay at home.

So, they get little sunlight. Moreover, aging can lower skin's capacity to convert vitamin D to its active form. Doctors usually suggest a good liquid multivitamin. To increase the absorption rate, liquid supplements are prescribed, as they have a better absorption rate as compared to the pill form.

Vitamin D deficiency implies that the person will be able to absorb only 10 to 15 percent of the calcium from his diet. An individual with adequate vitamin D is able to absorb 30 percent calcium from the food.

In healthy individuals, 30% absorption rate can be noticed. During pregnancy, lactation and growth spurts (for example, in teenagers), the body responds automatically and the absorption rate increases up to 80 percent.

• Intake of liquid vitamin supplements or pills.
• Balanced diet that includes food rich in vitamin D.

• Maintaining correct weight. Studies show that obese are prone to vitamin D deficiency. As the vitamin sets deep in the fat tissues, body cannot use it effectively.

• The diet should be rich in minerals too. For instance, without adequate supply of calcium, magnesium, zinc and other minerals, vitamin-D supplementation may withdraw calcium from the bone and will allow uptake of toxic minerals.

• Regular intake of vitamin A, vitamin K and boron boosts the process of absorption of vitamin D.

• Kidney dysfunction affects the process of absorption of this vitamin. Similarly, people who have severe liver problems will not be able to assimilate vitamin D (because it is a fat-soluble vitamin and liver helps in fat digestion). 

People who have intestine problems, are usually vitamin D deficient, because the intestines cannot absorb the nutrients properly. Prompt diagnosis and correct treatment will help to avoid health complications.

• Excessive use of alcohol, caffeine, sugar, tobacco, etc. can affect liver and kidney health, so should be avoided.

• Because of increased levels of polyunsaturated and monounsaturated fatty acids in diet, the process of binding of vitamin D to D-binding proteins is severely affected. Saturated fats such as those found in butter, tallow and coconut oil and the omega-3 fats do not have this effect. 

Vitamin D absorption and utilization is thus influenced by the kinds of fats you consume. But you cannot consume saturated fat in excess as it is harmful for your health. You need to consume all types of fats in proper proportions. This implies the importance of balanced diet.

As seen above, your body can produce vitamin D. But people from different descents can produce different amounts of vitamin D due to the different pigmentation.

For instance, a Caucasian may require 20 minutes of sunlight, 2-3 times per week to obtain sufficient vitamin D while an African-American with deep skin pigmentation may need double or triple the frequency and duration to get the similar effect.

The frequency and duration will also vary according to the time of day, season, weather condition (cloudy or sunny) and location (stronger sun intensity on and near equator).

Moreover, the intensity of the sun is at its strongest between 10am to 4pm. Remember, overexposure to the sun during this time should be avoided as chronic excessive exposure to sunlight increases the risk of skin cancer. Although vitamin D prevents a number of cancers, moderate sun exposure is recommended.

How much of vitamin D your body will be able to absorb depends upon your age and overall health. Those who exercise regularly, have healthy digestive system. It is noticed that modern lifestyle is responsible for poor digestive health.

City life, working in offices and factories, screening out ultraviolet light with glass windows, wearing more clothing when farming, using sun screens and dark glasses all contribute to a vitamin D deficiency. Human body receives ultraviolet light through the eyes and skin.

Studies show that ultraviolet deprivation may be responsible for the dramatic increase in cancer seen in certain parts of Africa. According to the studies, the Africans who could not absorb vitamin D through eyes because of sunglasses suffered from ultraviolet light deficiency. Black skinned people do not absorb much ultraviolet rays through their skin.

Thus, several factors are involved in the process of absorption of vitamin D. Certain changes in lifestyle, moderate exposure to the sun and simple dietary alterations can help solve the problem of scarcity of vitamin D in body.