Apart from overall health, the most frequent reason to take omega-3 fish oils is to lower cholesterol. As high cholesterol is seen as an indication of heart disease, lowering cholesterol and LDL is seen as healthy. As is often seen with health research, simple associations can easily become causation. It is important to note fish oils can lower heart disease without affecting cholesterol levels. For more than 100 years a direct link between high cholesterol levels and low thyroid function. Many examples were given in the 1930s and 1940s that showed a decline in cholesterol after correcting a thyroid deficiency;
“THE EXISTENCE of a relationship between thyroid II function and serum cholesterol level is well established. The writers have reported that the concentration of serum cholesterol of children with hypothyroidism before treatment varied from 145 to 660 mg. per cent, whereas in normal children it varied from 96 to 308 mg. per cent (1). The onset of thyroid treatment was followed by a marked drop in serum cholesterol of hypothyroid patients”
Sterol Balance in Hypothyroidism. WALTER FLEISCHMANN, M.D., LAWSON WILKINS, M.D., EDWARD SMETANA. The Journal of Clinical Endocrinology & Metabolism, Volume 1, Issue 10, 1 October 1941
“Thyroid administration produced a sharp drop in serum cholesterol in every case. This was accompanied by a rise in the basal metabolic rate.”
A LONG TERM STUDY OF THE VARIATION OF SERUM CHOLESTEROL IN MANI By KENNETH B. TURNER AND ALFRED STEINER. 1938
“Plasma cholesterol levels were significantly increased in hypothyroid animals. After thyroxine administration, plasma cholesterol levels were reduced to levels observed in euthyroid controls”
1986 Dec;35(12):1085-9. doi: 10.1016/0026-0495(86)90019-3. The effect of hypothyroidism and thyroxine replacement on hepatic and intestinal HMG-CoA reductase and ACAT activities and biliary lipids in the rat. F J Field, E Albright, S N Mathur
HMG-CoA reductase activity
Fish oils lower cholesterol by decreasing the enzymes that make cholesterol in the liver. One of the main enzymes that is reduced by fish oils is the enzyme HMG-CoA reductase. One study saying;
“HMG-CoA reductase activity was decreased in the distal two-thirds of the intestine in animals fed the menhaden oil compared to activities observed in controls.”
Field FJ, Albright EJ, Mathur SN. Effect of dietary n-3 fatty acids on HMG-CoA reductase and ACAT activities in liver and intestine of the rabbit. J Lipid Res. 1987 Jan;28(1):50-8. PMID: 3559400.
“The total cholesterol level was significantly increased 15% two days after the testosterone injection (p = 0.007). This is the first time a perturbation in the lipoprotein profile is observed after only a single dose of testosterone. Moreover, the HMGCR mRNA and protein expression was induced by testosterone in vitro and in vivo, respectively.”
Single dose testosterone increases total cholesterol levels and induces the expression of HMG CoA Reductase. Nina Gårevik, Cristine Skogastierna, Anders Rane & Lena Ekström. Substance Abuse Treatment, Prevention, and Policy volume 7, (2012)
“HMG-CoA reductase activity was decreased in the distal two-thirds of the intestine in animals fed the menhaden oil compared to activities observed in controls.”
“Because statins are less effective in hypothyroid patients whose HMG-CoA reductase activity is already reduced by the hypothyroid state, the AACE, the FDA, and the NCEP guidelines recommend that hypercholesterolemic patients undergo testing for thyroid disease before starting therapy with an HMGCoA-reductase inhibitor.”
FALL 2001 PREVENTIVE CARDIOLOGY An Association Between Varying Degrees of Hypothyroidism and Hypercholesterolemia in Women: The Thyroid-Cholesterol Connection Stanley Feld, MD; Richard A. Dickey, MD
Lowering Cholesterol By Reducing HMG-CoA reductase Is Not Healthy
Both statins and fish oils (and other PUFAs) lower HMG-CoA reductase activities. This is one reason why fish oils and statins (and omega 6) lower the protective hormones like pregnenolone, progesterone and testosterone. If cholesterol production is lowered, less protective hormones can be made, as is often observed in old age. With healthy cholesterol and thyroid levels, pregnenolone can be formed from cholesterol. From pregnenolone, progesterone and testosterone can be formed. See the formation of the steroid hormones below;
Androgen Physiology: Receptor and Metabolic Disorders. Iain J McEwan, PhD and Albert O. Brinkmann, PhD.