Vitamin B6 is an essential cofactor for over 100 enzymatic reactions. We need abundant B6 to keep what is left of our dopaminergic neurons as healthy as possible, especially since they are already compromised by Parkinson's. Levodopa medication depletes vitamin B6. B6 is only present in foods in low milligram amounts, so supplementation is usually necessary if we are taking levodopa medication. Failure to do so is likely to result in B6 deficiency, which may increase Parkinson's progression. It can ultimately result in no B6 at all, with dire consequences:
Epilepsy due to no B6 left: Refractory Seizures Secondary to Vitamin B6 Deficiency in Parkinson Disease: The Role of Carbidopa-Levodopa karger.com/Article/FullText...
"A 78-year-old gentleman with a 6-year history of Parkinson disease (PD) on carbidopa-levodopa, ... presented with new-onset myoclonus and focal to bilateral tonic-clonic seizures."
What are bilateral tonic-clonic seizures? Epilepsy: epilepsy.com/what-is-epilep...
"The bilateral tonic-clonic part usually begins with stiffening of the muscles (called the tonic phase).
• Air being forced past the vocal cords causes a cry or groan. The sound probably does not reflect pain or distress, because the person is not aware at this point.
• The person loses consciousness and falls to the floor.
• The tongue or cheek may be bitten, so bloody saliva may come from the mouth.
• Breathing can be temporarily impaired, and the person may look blue in the face.
Jerking movements happen next (called the clonic phase).
• The arms, legs, and face begin to jerk quickly and repeatedly; bending and relaxing at the elbows, hips, and knees can be seen.
• After a few minutes, the jerking slows and stops.
A person may lose control of their bladder or bowel as the body relaxes"
Back to the prior reference:
"Five months prior, he began experiencing a more rapid progression of his PD symptoms and an overall decline in functional status notable for worsening off periods, depression, and anorexia. His response to treatment with carbidopa-levodopa grew less robust despite increasing dosages.[Presumably due to a worsening B6 deficiency] ...the vitamin B6 level came back as undetectable at <1 μg/dL. ...intravenous B6 was initiated. Following introduction of these interventions, the patient had no further epileptic events."
Lest you think this is a one-off case this is not so: sciencedirect.com/science/a...
"Abnormal B6 levels have been reported in 60 of 145 PwPD (41.4% relative frequency). Low B6 levels were reported in 52 PwPD and high B6 levels were reported in 8 PwPD. There were 14 PwPD, polyneuropathy and low B6. There were 4 PwPD, polyneuropathy and high B6. There were 4 PwPD, epilepsy and low B6. Vitamin B6 level was low in 44.6% of PwPD receiving levodopa-carbidopa intestinal gel and in 30.1% of PwPD receiving oral levodopa-carbidopa." [emphasis added]
Once again for emphasis: There were 4 [People with] PD, epilepsy and low B6.
Epilepsy is no joke and neither is polyneuropathy: merckmanuals.com/home/brain...
"A pins-and-needles sensation, numbness, burning pain, and loss of vibration sense and position sense (knowing where the arms and legs are) are prominent symptoms. Because position sense is lost, walking and even standing become unsteady. Consequently, muscles may not be used. Eventually, they may weaken and waste away. Then, muscles may become stiff and permanently shortened (called contractures)...
Polyneuropathy often affects the nerves of the autonomic nervous system, which controls involuntary functions in the body (such as blood pressure, heart rate, digestion, salivation, and urination). Typical symptoms are constipation, sexual dysfunction, and fluctuating blood pressure—most notably a sudden fall in blood pressure when a person stands up (orthostatic hypotension). The skin may become pale and dry, and sweating may be reduced. Much less often, control of bowel movements or urination is lost, leading to fecal or urinary incontinence."
Neuropathy can also be caused by B12 deficiency. Testing for B12 levels does not reliably detect deficiency so I recommend everybody supplement B12.
B6 supplementation has acquired a bad reputation in the medical community:
B6 supplementation has acquired a bad reputation in the medical community because the cheap, inactive, common form of B6, pyridoxine, is toxic in quantity. It occupies binding sites that require the active form of B6 - P5P. In so doing it creates a situation similar to B6 deficiency. As a result pyridoxine can cause neuropathy. The active form of B6, P5P, is not toxic and is readily available. A distinction between these two is rarely made in medicine even though this distinction is vital. Conventional lab blood tests only check the active P5P version of B6. The levels of potentially toxic pyridoxine are not known and not reported.
Note that this statement from the above reference: "There were 14 PwPD, polyneuropathy and low B6. There were 4 PwPD, polyneuropathy and high B6. " fails to distinguish what form of B6 supplementation resulted in the high B6.
Details of pyridoxine toxicity here: healthunlocked.com/cure-par...
Another reason why B6 has acquired a bad reputation -
Vitamin B2 (riboflavin) deficiency can cause B6 toxicity
Details here: healthunlocked.com/cure-par...
To avoid B6 toxicity due to B2 deficiency, supplement vitamin B2 in addition to B6. Vitamin B2 is non-toxic and Parkinson's patients are commonly deficient in B2. A small trial using 90 mg per day showed benefit for Parkinson's patients. I personally have started taking 100 mg daily. I recommend supplementation, especially if you are supplementing B6.
When To Take P5P
As stated, levodopa medication depletes vitamin B6. The reason for this is that if carbidopa encounters B6, the two will bind together irreversibly, inactivating both. The same goes for benserazide in the case of madopar. So if taken together orally, levodopa medication and B6 will inactivate each other. If possible, P5P should be taken 2 hours apart from levodopa medication. If that is not possible, separate P5P from levodopa with a meal.
How Much P5P To Take
Many people, myself included, can tolerate dosages similar to their intake of carbidopa - I personally take a daily dose of 70 mg of P5P, versus a daily intake of carbidopa of about 60 mg. This ensures I will always have an abundant supply of vitamin B6 in my body. I have been doing this for years without any ill effects.
Some cannot tolerate even low milligram daily amounts.This is almost certainly due to B2 deficiency but this has not been definitively proven. For that reason I cannot make a specific recommendation as to how much others should take.
If you have a cooperative medical team that is willing to do regular testing of B6 and B2 levels that may be helpful. It appears that the upper plasma level of B6 is easily exceeded for people who are supplementing. For those who have low tolerance of vitamin B6 this may be a good way to stay out of trouble. It is also possible it may cause undue alarm for those who have high tolerance, and their doctors.
All I can say in conclusion is supplement B2, and use your own judgment on dosage of B6. Be familiar with the signs of neuropathy so you can act quickly in case it arises.