If there is one vitamin in the world that can help optimize a person’s health and well-being, it’s vitamin D (also known as vitamin D3 or cholecalciferol). Traditionally, vitamin D deficiency was associated with the bone disease rickets, but since the disease is now rare, many assume vitamin D deficiencies do not exist. Nothing could be farther from the truth!

Fortunately, this very necessary vitamin can be made and absorbed into the body for free when time is spent in the sun—ultraviolet B (UV-B) light waves from the sun react with a form of cholesterol in our skin to create the vitamin D hormone. However, that may not be enough for most to achieve optimal health. Additionally, since many people around the world spend more time indoors than outdoors, achieving adequate blood levels from the sun is difficult and most need to supplement.

Thousands of studies over the last decade show health benefits when one optimizes vitamin D intake. These studies tell us that those with higher levels of vitamin D in their blood have lower risk for heart attacks, breast cancer, colon cancer, multiple sclerosis, type 1 and type 2 diabetes, high blood pressure and other health complications.  

Yet, avoiding the sun is a common goal for many.  Many people around the world, usually on the advice of a physician, take pains to limit their time in direct sunlight.  This is done in an attempt to prevent the essentially non-life threatening basal cell and squamous cell skin cancers. Melanoma, the dangerous form of skin cancer, affects 1 in 80 people.  However, half of melanoma skin cancers occur in non-sun exposed areas of the body. 

In an attempt to avoid being that 1 in 80 people who get melanoma, we are actually increasing our risk for breast cancer (1 in 9), colon cancer (1 in 18) and prostate cancer (1 in 6) by limiting our exposure to vitamin D- producing sunrays.

Who is Deficient?

In my Southern California medical practice,  a place where we have sunny skies more than 300 days per year, four in five (80 percent) of my patients have clinical vitamin D deficiency, defined by a blood level 30 ng/ml (75 nmol/l)  or lower.  

The reason for this is that few people spend the required 15 to 20 minutes each day in the sunlight, allowing their face, arms and legs to be exposed to the ultraviolet light.   Up to 90 percent of people around the world are deficient. Those with more melanin, which is responsible for darker pigmented skin, require up to 30 minutes in the sun to generate vitamin D. Those over age 65 years also require more time outdoors to generate vitamin D due to changes in skin elasticity.

 Vitamin D is made by sun-exposed skin only during certain times of the day.  Primarily, if your shadow is “shorter” than you are tall, which is usually between 10AM to 2PM, Vitamin D production occurs.  Interestingly, this is also when solar energy panels make the most energy, too!  

Those who apply sunscreen prior to going outdoors block the sun’s rays from hitting the skin and generating vitamin D. Sunscreen should be applied after getting 15 to 30 minutes of sunlight exposure.

What are the Risks of Low Vitamin D Levels?

High Blood Pressure (Hypertension)

High blood pressure affects one in four adults. Worldwide, 1 billion people have high blood pressure, which is a leading risk factor for heart attacks, congestive heart failure and strokes.  While there are many reasons a person develops high blood pressure, studies show that men with lower levels of vitamin D are six times more likely to have hypertension while women were almost three times more likely. Maintaining a healthy weight, consuming a diet high in fruits and vegetables and doing routine exercise helps control blood pressure, too.

 So, what can vitamin D do? Scientific studies show vitamin D helps relax the blood vessels, which carry blood throughout our body, resulting in lower blood pressure. Vitamin D deficiency also likely accounts for a major reason those with increased skin pigmentation are at higher risk for high blood pressure. 

Heart Attacks

Heart disease is a leading killer in the United States, Europe and Asia. In the United States, it accounts for almost 1 million deaths each year. A Harvard University study showed that people with higher levels of vitamin D in their blood had 80 percent less risk of heart attacks when compared to those with the lowest blood levels.

 A study from Germany showed those with lower vitamin D blood levels were five times more likely to die from sudden cardiac death when compared to those with higher vitamin D blood levels. Many other studies have shown similar results. 

A 2017 study concluded “… the levels of blood vitamin D were significantly lower in heart attack patients, especially in America and Asia, and sufficient blood vitamin D levels might protect against the occurrence of heart attacks.”

Breast Cancer

Breast cancer will affect one in nine women during their lifetime. Mammograms help detect existing cancer, but preventing cancer from forming should be the priority, not simply trying to find it early.

 While consuming a healthy diet while maintaining a normal weight also helps prevent breast cancer, studies show that vitamin D can also be of value. A 2007 study from the University of California San Diego showed a 50 percent reduction in breast cancer in women who had vitamin D levels greater than 52 ng/ml (125 nmol/l). Another study showed that those women who lived in areas with more sunlight exposure had a 25 to 65 percent reduction in breast cancer. 

Numerous other studies have shown the benefits of vitamin D in reducing breast cancer.  A July 2017 study of almost 51,000 women showed supplementation with vitamin D reduced the risk of breast cancer by 21 percent in women who were postmenopausal (i.e. no longer having their monthly menstrual cycle).

Colon and Stomach Cancer

According to the American Cancer Society, colon cancer accounts for 8 percent of all cancer deaths in men and 9 percent of all cancer deaths in women. Worldwide, more than 1.3 million cases of colon cancer occurred in 2016. Fortunately, the majority of cases can be prevented.

 In addition to a healthy, high fiber diet, vitamin D may help prevent colon cancer. Scientists showed that those who live in areas with more sunlight had lower rates of colon cancer. Two studies, published in 2005 and 2007, showed that those with more vitamin D in their blood could decrease colon cancer risk by 50 percent. Another study concluded more vitamin D resulted in 60 percent less cancer.

 A 2014 study showed that those diagnosed with colon cancer and who had higher levels of vitamin D in their blood, were less likely to die from the disease than those with lower levels of vitamin D.  Similarly, a 2016 study showed stomach cancer was almost five times more common in those with a vitamin D deficiency.

Other Conditions Associated with Vitamin D Deficiency

Numerous other studies show those with lower vitamin D levels have higher rates of the following:

  • dementia
  • strokes
  • peripheral artery disease
  • prostate cancer
  • ovarian cancer
  • pancreatic cancer
  • fibromyalgia
  • falls
  • fractures
  • multiple sclerosis
  • lupus
  • rheumatoid arthritis
  • asthma
  • autism
  • psoriasis

The importance of vitamin D is obvious, and supplementation is crucial to your health.

What about Vitamin D toxicity?

There is no such thing as true “vitamin D toxicity”. However, those who take in excess of 10,000 IU of vitamin D daily for a prolonged period of time may absorb too much calcium resulting in elevated blood calcium levels and increased kidney stones. Those with chronic kidney disease, high blood calcium levels, and lymphoma need to consult with their physicians before starting vitamin D supplementation.

Know your Vitamin D Level

Ask your doctor to check your vitamin D blood level. She will need to order a vitamin D 25-OH blood test.  Most labs report normal results being 30 ng/ml (75 nmol/l) to 100 ng/ml (250mmol/l).  An optimal vitamin D blood level should be 50 ng/ml to 100 ng/ml (125 nmol/l to  250 nmol/l).


Most deficient adults will need to take a daily dose of Vitamin D (cholecalciferol) ranging 2,000-5,000 IU of Vitamin D. Some may need more.  Pregnant women and mothers who are breastfeeding should also consider supplementing with vitamin D at 5,000 IU daily. Vitamin D can be taken by most healthy children from 1 to 18 years of age. The usual dose is between 1,000-2,000 IU daily. 

Supplementation with vitamin D is crucial year round. However, it is even more important during the seasons of the year where sunlight is minimal.  Some doctors may recommend a vitamin D2 (ergocalciferol) prescription, which is 50,000 IU once weekly.  Based on the research, Vitamin D3 is clinically more effective and the preferred supplement.   

You can also increase your vitamin D levels by spending 15 minutes in the sun each day, without sunscreen, allowing your arms, face and legs to be exposed. Routine physical activity outdoors has a lot of health benefits.

Preventing chronic disease is the key to longevity and a quality life.  Daily vitamin D supplementation is that one vitamin that can actually help us achieve this goal


The above information is for educational purposes only. Always consult with your own personal physician or qualified healthcare professional regarding health matters you may have.  The products and claims made about specific products on or through this site have not been evaluated by the United States Food and Drug Administration and are not approved to diagnose, treat, cure or prevent disease. Read more about iherb.com’s disclaimer. 


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