Vanadium is a mineral that is not one of the Essential Mineral compounds, but is sometimes ingested in the diet. Can be found in bone tissues, Vanadium may influence glucose metabolism in an anti-diabetic manner.
Sources and Structure
Vanadium is what is known as an 'ultratrace' mineral in human nutrition. It is not one of the classical 24 vitamins and minerals, although it is needed for certain reactions in the body, such as formation of a pervanadate requierd for phosphorylation of some protein receptors. Typically between 6-20mcg of vanadium are consumed daily, mostly via peppers and seafood.
Vanadium has a history of usage in diabetes treatment, where oral administration of sodium vanadate preceded the discovery of insulin in 1921.
Vanadium, as vanadate in vivo inhibits the P-type phosphorylated ATPases and protein tyrosine phosphatases (PTPs). The dose to inhibit ATPases, however, is clinically significant only in toxic levels. Inhibition of PTP increases various tyrosine phosphorylation processes (as the phosphatases were inhibitory enzymes in phosphorylation).
Various effects come from PTP inhibition, such as inhibition of System A Amino Acid uptake into cells which transports neutral AA It can increase glucose uptake and GLUT4 mobilization via a phosphoinositol-3-kinase (PI3K) independent pathway (unlike insulin). The mechanism of action for vanadium acting as an insulin mimetic is increased general phosphorylation acting upon insulin receptor tyrosine kinase (of which get phosphorylated under the influence of insulin, as well as PTP inhibition).
Interactions with Glucose Metabolism
Vanadium containing compounds are known to inhibited protein tyrosine phosphatases (PTPs) as vanadium containing compounds tend to form a trigonal bipyramidal structure that can either act as a competitive inhibitor of phosphoryl transfer (which is the case for sodium orthovanadate) or an oxidizer of the cysteine residue of the PTP loop (peroxovanadate complexes). Similar to other PTP inhibiting compound (PTP1B inhibitors include berberine and ursolic acid) vanadium can prolong signalling through the insulin receptor via preventing the negative regulation of IRS-1 degradation, which is induced downstream of insulin receptor signalling (via mTOR signalling to S6K1) and works via PTPs to suppress and stimulate the degradation of IRS-1 as a form of negative feedback.
1mmol/L sodium orthovanadate appears to enhance signalling (L6 myocyte) by around 25% and is associated with inhibiting the decline in PI3K/IRS-1 complex activity, but has been noted to not inhibit the loss in mass of IRS-1.
Insulin eventually suppresses its own signalling via stimulating PTP enzymes (including PTP1B) which degrade IRS-1, the degration of IRS-1 then curtails further insulin signalling. Vanadium, like other PTP inhibitors, can prolong the signalling of insulin by preventing the degradation of IRS-1
One study that had separate groups of persons with Type II Diabetes and Healthy but obese controls noted that 100mg of Vanadium for 3 weeks was able to suppress glucose output from the liver in both groups, but only the diabetic group experienced an increase in insulin sensitivity while healthy controls had no significant changes in blood glucose parameters.
One human study (n=14) with 40-50yr old persons with Impaired Glucose Tolerance given 50mg twice daily (100mg daily) for a period of one month (30 days) noted that, in response to a euglycemic-hyperinsulinemic clamp, that vanadium treatment failed to improve insulin sensitivity and led to a small but significant increase in triglycerides.
In persons without Type II Diabetes, the effects of Vanadium supplementation appear to be lesser to the point of ineffective
A study in type II diabetics (n=6) noted that after vanadium administration at 100mg daily during weeks 3-5 of a 7 week study (with placebo given for the beginning and final two study) noted that testing after 3 weeks of Vanadium administration was associated with increased glucose uptake and insulin sensitivity which was still noted 2 weeks after cessation of vanadium; these improvements were accompanied by a decrease in HbA1c from 9.6+/-0.6% to 8.8+/-0.6%. Using Vanadium (as sulfate) at 150mg for 6 weeks was associated with a 20% reduction in fasting blood glucose and a decrease of HbA1c from 8.1+/-0.4 to 7.6+/-0.4%. Although this study noted a reduction in endogenous glucose production by 20% in diabetics, the correlation of this reduction to the reduction in fasting blood glucose was r=0.6.
However, the quality of these studies has been brought into question. This systemic review aimed to assess all double blind placebo-controlled studies on Vanadium and preliminary ended their search when they found none. Studies that existed, and those cited above, tend to have no placebo group and are limited to small samples sizes; their significant results have much less statistical power than other compounds.
Although it shows some benefit, the studies that suggest this benefit are low powered and Vanadium has less good evidence for its usage despite the amount of human interventions
Cholesterol and Triglycerides
100mg daily for 30 days in persons with impaired glucose tolerance failed to modify LDL-C, HDL-C, or total cholesterol while it led to a slight increase in triglycerides from 1.4+/-0.6mmol/L to 1.7+/-0.5mmol/L.
One study using rapamycin (inhibitor of mTOR; used in this study to inhibit IRS-1 degradation which is a negative regulator of insulin signalling) noted that rapamycin and sodium orthovanadate (1mmol/L) were synergistic in increasing glucose uptake into an L6 myocyte in the presence of insulin from 26.42+/-3.73% (seen in vanadium alone) to 97.83+/-8.54% (combination; rapamycin alone caused 39.9+/-3.39% uptake). This was due to inhibiting degradation of IRS-1 and prolonging signalling through the insulin receptor, which promoted PI3K induced glucose uptake, and was probably since vanadium could inhibit the degradation of PI3K/IRS-1 association (rapamycin ineffective) while rapamycin preventing the actual degradation of protein content of IRS-1 (vanadium ineffective).