Vitamin D is important for the health of every organ in our body. Learn all about vitamin D from a leading expert, Dr. Sarfraz Zaidi, MD,  a man who literally wrote the book on vitamin D, “Power Of Vitamin D.”

Vitamin D – A Hormone

You may be surprised to learn that it is actually not a vitamin but a hormone.

In general, a hormone is something that our body synthesizes, whereas a vitamin is something that we ingest in food.

Vitamin D is synthesized from cholesterol in our skin, upon exposure to UVB (Ultraviolet B) rays of the sun.

Natural Sources Of  Vitamin D

Sun is the best natural source of Vitamin D. On the other hand, food provides us with only small amounts of vitamin D.

Pandemic Of Vitamin D Deficiency

I started investigating vitamin D levels in my patients starting in 2001. This observational study continued over the next 17 years, in over 1200 patients. To my utter surprise, the vast majority of my patients turned out to be low in vitamin D, although they were living outdoors for at least 15 minutes, three times a week in sunny southern California. Most also took recommended doses of vitamin D. Many ate fish two to three times a week. According to traditional knowledge, they should not have been low in Vitamin D.

My experience is in line with other researchers. For example, a study from the National Institutes of Health, USA, analyzed the data on vitamin D status in the U.S. adult population from 2000-2004, which showed that 50-78% of Americans were low in vitamin D.

Not only Americans, but people all around the world are suffering from vitamin D deficiency.

It is clear that Vitamin D deficiency is the true pandemic of our times. It is perhaps more common than any other medical condition at the present time.

What Are The Causes For The Pandemic Of Vitamin D Deficiency? 

1. Modern Lifestyle

The main reason we’re facing pandemic of vitamin D deficiency is our modern lifestyle, which minimizes our exposure to the sun.  Our technological revolution has dramatically changed our lifestyles.

Most people work indoors. They leave their homes early in the morning and return home around sunset or even after dark (especially during wintertime). Even at lunch, most people drive to a restaurant or stay inside to eat.

Many people spend their lunch break in their office. Over the weekend, we watch TV or surf the internet for entertainment.

Teenagers usually stay indoors hooked to a computer, smart phone or other electronic gadgets rather than going outdoors and playing real sports.

While shopping, people are mostly indoors thanks to huge grocery stores and shopping malls.

Many of the elderly live in assisted living facilities or nursing homes and don’t get any sun exposure.

Just observe yourself.  How often do you, your family and friends stay indoors while carrying out usual activities of daily living?

2. Sun Phobia

Over the last 50 years or so, sun avoidance has been successfully drilled in the minds of the general public. People are simply scared of the so-called ill-effects of the sun including skin cancer, wrinkles and aging spots. Due to sun phobia, people avoid sun exposure at all costs. When we go outside for even a little while, we make sure to apply sunscreen. Parents compulsively apply sunscreen before they allow their children to go outdoors. Many people don’t realize that sunscreen also prevents vitamin D synthesis in the skin.

3. Obesity

Vitamin D is fat soluble. Therefore, it gets stored in the fat in your body. In obese individuals, there is excessive storage of vitamin D in fat. Consequently, the circulating level of vitamin D is low in these individuals.

Obesity has reached epidemic proportions in the USA, and the rest of the world is also catching up in this regard. The pandemic of obesity is contributing to the pandemic of vitamin D deficiency. It’s interesting to note that in most cases, obesity too is a product of our modern lifestyle.

4. Medical Illnesses

Malabsorption:

Because vitamin D is fat soluble, vitamin D deficiency can develop in medical conditions that cause malabsorption of fat, such as surgical resection of the small intestine and stomach, chronic pancreatitis, pancreatic surgery, Celiac sprue, Crohn’s colitis and cystic fibrosis.

Liver and Kidney Diseases:

Vitamin D from the blood is taken up by the liver where it is transformed into 25 (OH) Vitamin D which in the kidneys is further transformed into 1,25 (OH)₂ Vitamin D.  Therefore, vitamin D deficiency develops in chronic liver disease such as cirrhosis and in chronic kidney disease.

5. Medications

Some medications can further decrease vitamin D level.

These medications include Phenytoin (brand name Dilantin), Phenobarbital,  Rifampin, Orlistat (brand names Xenical and Alli), Cholestyramine (brand names Questran, LoCholest and Prevalite) and Steroids

I often see patients who have been on these drugs for a long time, yet they’re completely unaware these drugs can rob them of vitamin D.

6. Current Recommendations on Vitamin D Intake are Inadequate

Many people taking vitamin D assume that their vitamin D level should be okay because the label on their vitamin bottle says it meets 100% of the daily requirements. In my observation, this misconception is one of the major reasons for vitamin D deficiency.

Vitamin manufacturers follow government guidelines for the daily recommended amounts of various vitamins and minerals. As of 2026, the recommended daily allowance of vitamin D in the USA is: 400 I.U. (International Units) from birth to age 1, then 600 I.U. from age 1 until age 70, and 800 I.U. if you are older than 70.

Based on my vast clinical experience, most people need a much higher daily dose of vitamin D –

5000 IU to 10,000 IU – to obtain an optimal level of vitamin D.

Symptoms of  Vitamin D Deficiency

Vitamin D deficiency is linked to an increased risk of:

• Osteoporosis (weak bones)
• Tooth fractures
• Infections
• Cancer
• Heart disease
• Diabetes, (both Type 1 and Type 2)
• Depression
• Autoimmune diseases such as asthma, rheumatoid arthritis, lupus, Multiple Sclerosis, Hashimoto’s thyroiditis, Graves’ disease etc.

Vitamin D Supplements

Vitamin D deficiency is primarily due to our lifestyle that forces us to avoid the sun for one reason or another.

Therefore, from a practical standpoint, we can take Vitamin D supplements to achieve a good level of Vitamin D.

How Much Vitamin D3

Following are the doses of vitamin D3 to get a good level of vitamin D, based on my extensive clinical observations in more than 1200 patients over a period of 17 years:

• 5000 IU per day if your weight is more than 100 Lbs.
• 10,000 IU per day if you are above 200 Lbs.

Vitamin D3 With K2

It is better to take Vitamin D3 in combination with Vitamin K2 because both work in synergy and may help build bones and teeth, support heart health, boost the immune system, and prevent cancer, among many other benefits. The usual dose of Vitamin K2 for adults is 100 – 200 mcg per day.

Vitamin D Toxicity

In my extensive clinical experience of treating thousands of patients with Vitamin D deficiency, I did not see any Vitamin D3 toxicity. There have been a handful of case reports of vitamin D toxicity in people who were taking doses of more than 80,000 IU of Vitamin D3 per day.