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The Power of Vitamin D – The Sunshine Vitamin


Vitamin D is one of the most critical vitamins for overall health and longevity.

Your body needs vitamin D, but how much and how do you get it?

The Sunshine Vitamin

Vitamin D is both a nutrient and a hormone our bodies make. It is a fat-soluble vitamin (a vitamin that can dissolve in fats and oils) that helps the body absorb and retain calcium and phosphorus, both critical for building bone. Vitamin D also reduces cancer cell growth, boosts the immune system, and reduces inflammation, and scientists are actively investigating other possible functions.

Recommended Amount

Worldwide, an estimated 1 billion people have inadequate vitamin D levels, and deficiencies can be found in all ethnicities and age groups. In industrialized countries, doctors see the resurgence of rickets, the bone-weakening disease primarily eradicated through vitamin D fortification. In the U.S., Vitamin D deficiency iwidespreadon, affecting approximately 42% of the U.S. population.

There is a lot of scientific debate around how much vitamin D people need each day and the optimal level to prevent disease. Experts disagree on what low vitamin D means, and some laboratories define it as below 30 nanograms per milliliter (ng/mL), while others set it at below 50 ng/mL.

The Recommended Dietary Allowance for vitamin D  for adults 19 years and older is 600 IU (15 mcg) daily for men and women, and for adults >70 years, it is 800 IU (20 mcg) daily.

Many doctors argue this is well under what people need and recommend 4,000-5,000 IU (International Units) daily for adults and 500-1,000k IU per day for kids, or 35 IUs per pound of body weight.

For example, I weigh 120 lbs x 35 = 4,200 IUs daily (1 IU = 25 mcg)

Tip: Vitamin D  is absorbed best in your bloodstream when paired with high fat foods. For this reason, it’s recommended to take vitamin D supplements with a big meal to enhance absorption.

Evidence supports the benefits of consuming adequate vitamin D. However, there is still no consensus on the amount considered sufficient, which is why the U.S. Preventive Services Task Force (USPSTF) concluded that it isn’t helpful for most people to know their vitamin D level and why you must request to get your vitamin D checked when doing blood work.

Vitamin D and Your Health

The role of vitamin D in disease prevention is a popular area of research. Observational studies show a strong connection with lower rates of certain diseases in populations living in sunnier climates or having higher vitamin D levels. Still, straightforward answers about the benefit of taking amounts beyond the RDA are inconclusive. This may be due to different study designs, absorption of vitamin D , and different dosages given to participants.

So, can supplementing with vitamin D help boost our body’s defenses to fight the flu, and autoimmune diseases, improve cognitive function, and help strengthen our bones?

Here’s what the studies show.

Bone Fractures

Several studies link low vitamin D blood levels with an increased risk of fractures in older adults. Studies show Vitamin D3 plays a vital role in maintaining strong bones throughout life because it helps the body absorb and retain calcium critical for building bone.

A meta-analysis of 12 randomized controlled trials that included more than 42,000 people 65+ years of age, most women, looked at vitamin D supplementation and a placebo. Researchers found that higher intakes of vitamin D supplements—about 500-800 IU per day—reduced hip and non-spine fractures by about 20%. Lower intakes (400 IU or less) failed to offer fracture prevention.

Multiple Sclerosis

The rate of multiple sclerosis (MS) is increasing, with an unclear cause. However, a person’s genetic background plus environmental factors, including inadequate vitamin D and UVB exposure, have been identified to increase risk. Over 40 years ago, it was suggested that vitamin D played a role in MS. Rates of MS were much higher far north (or far south) of the equator than in sunnier climates. A prospective study of dietary intake of vitamin D found women with daily intake above 400 IU had a 40% lower risk of MS. In a study among healthy young adults in the US, White men and women with the highest vitamin D serum levels had a 62% lower risk of developing MS than those with the lowest vitamin D levels. The study didn’t find this effect among Black men and women, possibly because there were fewer Black study participants, and most of them had low vitamin D levels, making it harder to find any link between vitamin D and MS if one exists.

Another prospective study in young adults from Sweden also saw a 61% lower risk of MS with higher serum vitamin D levels. A prospective study among young Finnish women found that low serum vitamin D levels were associated with a 43% increased risk of MS. In future studies of persons with MS, higher vitamin D levels have been associated with reduced disease activity and progression. While several clinical trials are underway to examine vitamin D as a treatment in persons with MS, there are no clinical trials aimed at preventing MS, likely because MS is a rare disease and the trial would need to be large and of long duration. The current evidence suggests that low vitamin D may have a causal role in MS. If so, approximately 40% of cases may be prevented by correcting vitamin D insufficiency. Recent evidence has strengthened this conclusion that genetically determined low vitamin D levels predict a higher risk of multiple sclerosis.

Flu and the Common Cold

Some believe the flu virus goes away in the summer, but a virus doesn’t go away. The flu virus wreaks havoc in the winter, lessening in the summer because vitamin D levels are highest in summer.

Studies show children with vitamin D deficiency are more likely to get respiratory infections. In contrast, children exposed to sunlight have fewer respiratory infections, and adults with low vitamin D levels are likelier to report a recent cough, cold, or upper respiratory tract infection.

A randomized controlled trial in Japanese school children tested whether taking daily vitamin D supplements would prevent seasonal flu. The trial followed nearly 340 children for four months during the height of the winter flu season. Half of the study participants received pills that contained 1,200 IU of vitamin D; the other half received placebo pills. Researchers found that type A influenza rates in the vitamin D group was about 40% lower than in the placebo group; there was no significant difference in type B influenza rates.

The findings from this large meta-analysis have raised the possibility that low vitamin D levels may also increase the risk of Covid. Although there is no direct evidence on this issue because this is such a new disease, I believe avoiding low vitamin D levels is logical, unlike when politicians closed the beaches and parks.

Other Autoimmune Conditions (rheumatoid arthritis, psoriasis, Hashimoto’s, and more)

A randomized, double-blind, placebo-controlled trial following more than 25,000 men and women ages 50 and older found that taking vitamin D supplements (2,000 IU/day) for five years reduced the incidence of autoimmune diseases by about 22%, compared with a placebo. Autoimmune conditions observed included rheumatoid arthritis, psoriasis, polymyalgia rheumatica, and autoimmune thyroid diseases (Hashimoto’s thyroiditis, Graves’ disease).  The doses in these supplements are widely available and generally well-tolerated.

Cognitive Decline

In an analysis of more than 427,000 White European participants, a 54% higher risk of dementia was seen among participants with low vitamin D blood levels of <25 nmol/L compared with those with adequate 50 nmol/L levels.

Vitamin D and food

Ensuring your immune system is strong is crucial. Obtaining enough high-quality vitamin D through the diet or sunshine alone can be difficult. Most people only get 140 IUs daily from food alone, even less if they are vegan.

The primary natural source of vitamin D is through the sun, but many people have insufficient levels because they live in places where sunlight is limited or because they are indoors most of the day or use sunscreen. And only a few foods naturally contain vitamin D or are fortified with vitamin D.

Foods Rich In Vitamin D

Foods naturally rich in vitamin D3 are wild salmon, sardines, mackerel, tilapia, tuna fish, swordfish, trout with skin on, cod liver oil, and beef liver. Small amounts are found in egg yolks, milk, cereal, and orange juice fortified with vitamin D.

Certain mushrooms contain higher amounts of D2 due to intentionally being exposed to high doses of ultraviolet light.

Fun fact: to increase vitamin D levels in mushrooms, let them sit outside in the sun for 20-30 minutes.

The Difference Between Vitamin D3 and Vitamin D2 Supplements

Vitamin D supplements are available in two forms: vitamin D2 (“ergocalciferol” or pre-vitamin D) and vitamin D3 (“cholecalciferol”). Both are also naturally occurring forms that are produced in the presence of the sun’s ultraviolet-B (UVB) rays. Vitamin D2 is made from plants and found in fortified foods and supplements, and vitamin D3 is naturally produced in the human body and is found in animal foods.

There is an ongoing debate about whether vitamin D3 is better than vitamin D2. Some experts cite vitamin D3 as the preferred form as it is naturally produced in the body and found in most foods that naturally contain it.

Vitamin D from the sun

D3 can be formed when a chemical reaction occurs in human skin when a steroid called 7-dehydrocholesterol is broken down by the sun’s UVB light or so-called “tanning” rays. The amount of the vitamin absorbed can vary widely, but just because you’re in the sun doesn’t mean you’re absorbing it.

The following decreases exposure to UVB light and therefore lessens vitamin D absorption:

  • Using sunscreen can reduce vitamin D absorption by over 90%.
  • Wearing full clothing that covers the skin.
  • Spending a lot of time indoors.
  • People with darker skin are typically deficient in vitamin D due to having higher amounts of the pigment melanin, which acts as a natural sunscreen.
  • Older people have lower levels of vitamin D because 7-dehydrocholesterol levels decrease in the skin, and as some get older, they are likely to spend more time indoors.
  • Certain seasons and living in northern latitudes above the equator where UVB light is weaker.
  • The body stores vitamin D from summer sun exposure, but it only lasts a few months. By late winter, many people are deficient.
  • Generally, ordinary glass, such as your car or home windows, filters out UVB sun rays. Sitting by the window on a sunny day will not increase vitamin D intake. You have to be outside to soak up the sun’s rays.

Signs of Vitamin D Deficiency and Toxicity


Vitamin D deficiency occurs from a lack of sun exposure, not eating enough vitamin D, poor absorption, or a metabolic need for higher amounts. Other people at high risk of vitamin D deficiency include:

  • People with inflammatory bowel diseases like ulcerative colitis and Crohn’s disease disrupt normal digestion.
  • Vegans or people who cannot eat fish, eggs, or milk.
  • People who are obese tend to have lower vitamin D levels. Vitamin D accumulates in excess fat tissues but is not readily available for use by the body when needed. Higher doses of vitamin D supplementation are required in order to achieve a desirable blood level. Conversely, blood levels of vitamin D rise when obese people lose weight.
  • People who have undergone gastric bypass surgery typically remove the upper part of the small intestine, where vitamin D is absorbed.

Conditions resulting from prolonged vitamin D deficiency:

  • Rickets: A condition in infants and children of soft bones and skeletal deformities caused by failure of bone tissue to harden.
  • Osteomalacia: A condition in adults of weak and softened bones that can be reversed with supplementation. This is different than osteoporosis, in which the bones are porous and brittle, and the condition is irreversible.

Too Much Vitamin D

Vitamin D toxicity, also called hypervitaminosis D, is a extremely rare but potentially serious condition that occurs when you have excessive amounts of vitamin D. Vitamin D toxicity is usually caused by large doses of vitamin D supplements. The low amounts of the vitamin found in food are unlikely to reach a toxic level, and a high amount of sun exposure does not lead to toxicity because excess heat on the skin prevents D3 from forming.

Symptoms of toxicity:

  • stomach pain
  • fatigue
  • dizziness
  • constipation
  • bone pain
  • hardening of blood vessels and tissues due to increased blood levels of calcium, potentially leading to damage to the heart and kidneys.


Key Points

The “normal range for Vitamin D on your blood work is 30-100 ng/mL (nanograms per milliliter). So if your blood work shows 35 or 90, your Vitamin D levels are normal? That’s a wide range. You want your Vitamin D levels to be between 50-80 (ng/mL). Start supplementing if they are lower than 50.

To determine how many IUs (International Units) of vitamin D you need, multiply your weight by 35.

Vitamin D is a fat-soluble vitamin, meaning that it does not dissolve in water and is absorbed best in your bloodstream when paired with high fat foods. For this reason, it’s recommended to take vitamin D supplements with a meal to enhance absorption. I like to take my vitmain D with my eggs and avocado toast.

The metric for vitamin D is changing, and the FDA is moving away from IU to mcg to make it more standardized (1000 IUs = 25 mcg).

If there is reason to believe that levels might be low, such as having darker skin or limited sun exposure, I strongly recommend taking a supplement of 1000 or 2000 IU per day. This amount is now part of many standard multiple vitamin supplements and is inexpensive. This is the vitamin D my whole family takes.

If you want to check your vitamin D levels, call your doctor or click HERE to order an at-home lab test that arrives promptly at our door.

Ideally, you want to test your Vitamin D two times a year, in winter and summer.

If you have a question or want me to speak at an event, email me at or follow me on Instagram or Facebook.

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