Vitamin D — Are You Getting Enough of It?

Joseph R. Anticaglia MD
Medical Advisory Board

When I was about five years old, my mother would open the kitchen cabinet door, take out a dark bottle and come towards me with a spoon in her hand. She didn’t have to say anything.

— Oh, no. cod liver oil! Yuk!
— It’s good for you
— I don’t care.

Little did I realize or care about the benefits of vitamin D salvaged from the liver of cod fish. Today, and for many years, I have appreciated the myriad functions of this “sunshine” vitamin.

Vitamin D is usually classified a fat-soluble vitamin that makes it easier for the intestines to absorb calcium. We need calcium to build and maintain strong bones and to prevent bone fractures.

Children deficient in vitamin D may grow with soft bones unable to support their weight (rickets, bowed legs). Adults who do not get enough vitamin D may develop softening of their bones referred to as osteomalacia. In other situations, adults may lose bone mass, develop fragile bones and become more susceptible to fractures a condition called osteoporosis.

Low level of vitamin D is a danger to bones and too much calcium is a danger to soft tissue such as kidneys and arteries. Vitamin D helps to regulate these two extremes of hypocalcemia (too little calcium) or hypecalcemia (too much calcium).

Besides helping the intestinal absorption of calcium and bone health, there are other benefits of maintaining vitamin D level within a normal range. Population studies suggest, according to Dr. Sundeep Khosla of Mayo Clinic, that vitamin D plays a role in:

  • Protecting us against heart disease
  • Lessening the risk of getting cancer
  • Vitamin D might increase cognitive function
  • Could be useful in patients with depression
  • May lower the risk of diabetes
  • Might decrease the risk of autoimmune disease

You can get Vitamin D in three ways

  1. Through your diet,
  2. Taking supplements
  3. By way of the interaction between the sun and your skin.

Several different compounds make up the “D” vitamin family. Two of them are vitamin D2 (ergocalciferol) is made by plants and D3 (cholecalciferol) is made by humans.

Vitamin D, the Sun and the Skin

A form of cholesterol is naturally found in the skin, 7-dehydrocholesterol (7DHC). When the ultraviolet-B rays (UVB) of the sun hit the cholesterol in the skin, a chemical reaction takes place forming vitamin D3. This vitamin is converted into its active form by the liver and the kidneys. The active form of vitamin D3 (calcitriol) circulates in the bloodstream and is utilized where needed by the body.

Despite the importance of the sun in the synthesis of vitamin D, people should limit their exposure to the sun to minimize the risk of skin cancer. About 10 to15 minutes of sun exposure per day is enough to keep you from becoming vitamin deficient.

People living in northern latitudes or working many hours indoors, certain times of the day, shade or cloudy days can reduce or interfere with the production of vitamin D.

Vitamin D and Foods

The vitamin D we get from food or supplements require conversion by the liver and kidneys to become entirely active. That is why persons with liver or kidney disease are at a greater risk to develop bone disorders.

Not many foods are good sources of Vitamin D. Fatty fish such as tuna and salmon are the good sources. Egg yolks and beef liver provide small amounts of the vitamin.

Because of the relative scarcity of vitamin D in many natural foods, the government has mandated that certain foods be enriched with vitamin D and other vitamins. Milk and breakfast cereals are fortified with Vitamin D as well as other brands of foods and drinks.

Vitamin D and Supplements

Vitamin D2 and D3 are the two available forms used in supplements and fortified foods.

Vitamin D3 is manufactured when the ultraviolet B rays of the sun hit 7DHC, the cholesterol in the skin. Vitamin D2 is manufactured by the ultraviolet irradiation of yeast in plants.

Most people in the U. S. do not get adequate exposure to sunlight. Also, since food is not the optimal source of vitamin D, millions of Americans use supplements to get adequate amounts of vitamin D into their diet.

Although both forms of this supplement have been regarded as equivalent, it appears that D2 is less potent at higher doses. Vitamin D3 is the recommended supplemental form of vitamin D and one should consider taking vitamin K2 with this supplement… Talk to your doctor about the right dosage for you or your child.

Are You Getting Enough Vitamin D?

The millions of Americans have blood levels of vitamin D that is too low for bone growth and overall health. The 25-hydroxyvitamin D blood test is the best way to find out if you are vitamin D deficient or not.

Who is at Risk?

Breast fed infants, older adults and obese people are at an increased risk to experience vitamin D deficiency.

Individuals with liver or kidney disease are susceptible to vitamin D deficiency because they have difficulty converting vitamin D into its active form. People with intestinal problems causing malabsorption of nutrients are at risk for vitamin D deficiency.

Dark skin people, overuse of sunscreen, regular use of mineral oil as a laxative or persons who have undergone surgery for obesity are factors that can cut down on vitamin D production.

Is Vitamin D a Hormone?

Vitamin D is thought by many to be a prohormone, a substance that the body can convert into a hormone. It’s considered to be a hormone because of the way its active form — calcitriol works.

Calcitriol travels in the bloodstream targeting and regulating the activity of cells, tissues and organs. It influences the metabolism of calcium and phosphorus and other systems as noted above by Dr. Khosla.

Vitamin D deficiency remains a significant concern the United States. Mounting reports indicate that low levels of this vitamin may be linked to chronic conditions such as cancer and cardiovascular disease.

Here’s an important question for us to answer: “Is our vitamin D level within a normal range?” A simple blood test is the best way to get the answer.


  1. Ebeling, PR; Vitamin D and Bone Health: Epidemiologic studies; BoneKEY Reports 3; 2014
  2. NIH; Vitamin D; April 15, 2016;
  3. National Cancer Institute; Vitamin D and Cancer Prevention; October 21, 2013 U. S. Preventive Task Force; Vitamin D Deficiency; December 2016
  4. NIH; Vitamin D Fact Sheet; U. S. November 9, 2018
  5. Anticaglia, Joseph R; Vitamin Basics; Doctor’s Column, HC Smart, 2019

This article is intended solely as a learning experience. Please consult your physician for diagnostic and treatment options.