February 28, 2020

Cod liver oil, vitamin D and the Jewish mother

I was raised in a “shtetl” on the west side of Chicago, where communal life was in large measure under the direction of the Jewish Elders.  Religiosity dominated our daily life, including our interaction with family and friends.  Our community was also concerned about safety and health.  Medical care was expensive and generally inaccessible, so most treatment modalities were learned from family and friends.  One of these was cod liver oil.  With only one exception every year (Yom Kippur), my mother forced down my throat a large tablespoon of the most rancid, smelly oil ever created on this planet.  Motor oil would have probably tasted much better.  In retrospect, this was clearly done with concern and caring for my health and well-being, which was not obvious while I was belching and retching for an hour after the ingestion of this foul-smelling, fishy oil.  It was 30 years later before I ever ate fish again.

Cod liver oil was traditionally manufactured by filling a wooden barrel with fresh cod livers and seawater and allowing the mixture to ferment for up to a year before removing the oil.  Unfortunately, I once had a quick glimpse of this process at the rear of a fish market when I was a young child.  Aaach!  Today, cod liver oil is made by cooking and extracting the liver of this fatty fish during the manufacture of fishmeal.  The Jewish mother felt that this therapeutic product could have a positive effect on the health of the heart and the bone, as well as nourishment for the skin, hair and nails.  It also helped ease the pain and joint stiffness associated with arthritis, and the use of cod liver oil during pregnancy was associated with a lower risk of type I diabetes in the offspring.  In a recent Norwegian study, more than 68,000 female cancer patients who took daily cod liver oil supplements had significantly reduced mortality compared to women who did not take such supplements. 

Cod liver oil has been utilized for many centuries.  In addition to their diet, the Vikings used this oil as a lubricant to allow the transport of ships across land – the oil was smeared on logs which acted as rollers beneath the hull of the ship.

The ingredients in cod liver oil that are therapeutic include omega-3 fatty acids, vitamin A, and vitamin D.  Studies have shown that this product has the potential to reduce both the progression of cardiovascular disease and related mortality, including sudden cardiac death.  Researchers also found that people who suffer from depression who received a daily dose of 1 gram of an omega-3 fatty acid (found in cod liver oil) for 12 weeks experienced a decrease in their symptoms, such as anxiety, sadness and sleeping problems.

You now have a choice.  You could continue to take the cod liver oil, but now flavored and often in a capsule form, or you could just simply supplement with Vitamin D tablets (and add omega-3 fatty acids).  Low vitamin D status is extremely common worldwide because of low dietary intake and low skin production.  Suboptimal vitamin D levels contributes to the development of rickets, osteoporosis, falls, fractures and a multitude of other conditions.  Although consensus does not exist, it appears that circulating vitamin D levels greater than 30-32 ng/ml are needed for optimal health.  To achieve this, daily intake of at least 1000 IU of D3 daily are required, and it is probable that substantially higher amounts are needed to achieve normal values in a population basis.  Widespread optimization of Vitamin D status likely will lead to prevention of many diseases with attendant reduction of morbidity, mortality and expense.


A. Low vitamin D has long been associated with rickets and has a role in the pathogenesis of osteoporosis by way of calcium malabsorption.  Recent studies show that low Vitamin D levels are associated with higher fracture risk.  In addition, a dose effect was reported with greater Vitamin D intakes and higher achieved vitamin D concentrations, providing superior fracture reduction benefit.  Thus, low vitamin D status leads to adverse bone consequences, which can be corrected with supplementation.

B. Muscle function and falls.  Regardless of the mechanism, patients with osteoporosis/osteomalacia because of vitamin D deficiency develop muscle pain and weakness that is improved with vitamin D therapy.  Muscle biopsy in such people reveals atrophy of the fast twitch fibers, which may explain the increased fall risk in vitamin D deficient individuals.  Vitamin D replacement reduces this risk by more than 20%.

C. Cancer.  Vitamin D has antiproliferative and pro-differentiating effects on many cell types, which may reduce cancer risk.  Consistent with this, there is a body of literature which states that low vitamin D intake and /or less sunlight exposure leads to an increased risk of mortality from multiple types of cancer.  Prospective trials of vitamin D supplementation with cancer as an endpoint are very limited.  However, a small prospective study of postmenopausal women found calcium plus vitamin D3 at 1100 IU daily reduces overall cancer risk by approximately 60%.  To summarize, observational data in one small randomized trial find low vitamin D status to be associated with higher cancer risk.  Additional prospective studies are needed.

D. Other Conditions

1. Immunity. It is likely that vitamin D has immune modulating effects.  It has long been recognized that vitamin D deficiency is associated with respiratory infections, which perhaps contributed to the previous use of cod liver oil in anti-tuberculosis therapy.  Low vitamin D status is associated with an increased risk of autoimmune and potentially infectious diseases.  In addition, inflammation is increasingly becoming recognized as a contributor to the pathogenesis of various diseases, and vitamin D modulates inflammatory cytokine production.

2. Diabetes.  It has been suggested that endemic low vitamin D is contributing to the increased prevalence of diabetes mellitus.  Multiple potential mechanisms have been proposed, including vitamin D increasing insulin production/secretion.  Recent observational studies associate low Vitamin D status with both diabetes type I and type II.  Prospective studies of vitamin D supplementation are clearly indicated; it appears that low vitamin D status impairs glucose metabolism.

3. Heart Disease.  Observational studies report an association between low vitamin D and cardiovascular disease.  Potential mechanisms include a vitamin D effect on theendothelium, vascular smooth muscle, and/or cardiomyocytes – all of which possess the vitamin D receptor.  Prospective studies to further evaluate this reported association are needed.

4. Pain and headaches.  There are a few journal articles suggesting that vitamin D supplementations may help with headaches.

5. Alzheimer’s and Parkinson’s disease.  Some studies have demonstrated a link between
low vitamin D levels and cognitive dysfunction, and a few studies have shown low vitamin D levels to be linked to Parkinson’s disease.
In summary, low vitamin D status has been associated with a variety of diseases, and biologically plausible hypotheses exist to suggest a possible causal role.  However, until confirmed by randomized studies, it is wise to be cautious and recognize that association does not prove causation.

There are no randomized trials advocating a population screening approach, but it seems reasonable to at least measure 25-hydroxy vitamin D in those identified as being at high risk of vitamin D deficiency, and those for whom a prompt musculoskeletal response to optimization of vitamin D status could be expected.

Such groups include those with osteoporosis, a history of falls or high risk of falls, malabsorption such as with celiac disease, radiation enteritis, bariatric surgery, individuals with liver disease, and those requiring medications known to alter vitamin D levels (certain anticonvulsants).  Given the relationship of low vitamin D status with cancer, it also seems rational to measure vitamin D in those with malignancy.


Increasing exposure to sunlight would be an effective and free approach to improving vitamin D status.  However, this does not seem to be viable given widespread sun avoidance campaigns based on the association of UV exposure with skin cancer.

It could be argued that simple treatment of all individuals with vitamin D should be advocated, therefore making vitamin D measurement unnecessary.  But again, there is no expert consensus regarding this recommendation, nor is there consensus regarding a recommended dose.  Some recommend 800 to 1000IU daily, whereas some vitamin D experts suggest values over 2000IU per day.  Vitamin D dosing may differ by age in that older adults likely require higher vitamin D intake because of the lower capability of their skin to produce vitamin D with advancing age.  Similarly, clear differences exist between races, with African-Americans requiring higher intake than Caucasian-Americans.

Various “high dose” repletion approaches exist, such as 50,000 IU three times weekly or monthly.  There are additional reports of recommendations using more than 600,000 IU administered over two months, plus an additional clinical report of 50,000 IU once weekly for up to three years.

Available data find daily vitamin D supplementation to be less effective than expected at increasing vitamin D status, perhaps because of failure to reliably take the supplements.  A reasonable clinical “rule of thumb” is that the addition of 1000 IU of vitamin D3 daily can be expected to increase circulating vitamin D levels by approximately 10 ng/mL.  Keep in mind that it can take up to three to six months for serum vitamin D
levels to plateau following initiation of supplementation. 

Finally, after complaining to my mother about the nauseating taste of cod liver oil, she put this slimy, putrid medicine into a glass of orange juice, which, unfortunately, did not mask the taste.  It was yet another 30 years before I could drink orange juice again.  But just yesterday, I sat down to breakfast and I had a plate of geflite fish and a glass of orange juice.  I did not recall the terrible taste, but I was reminded of the love and concern my Jewish mother had for my health and welfare.